Dissertations / Theses on the topic 'Gold electrode'

The high quantum efficiency of photosynthetic reaction centers makes them candidates for use in solar energy harvesting devices. A bio-photovoltaic cell can be made by dissolving reaction centers and two mediators, such as quinone and cytochrome c, in the conductive electrolyte of an electrochemical cell. The mediators transfer the photo-generated charges to the electrodes upon illumination. So far such protein-based devices have shown low overall power conversion efficiency. Previously it has been shown that slow charge transfer limits the efficiency of these devices. Moreover, it has been observed that the cell response is dependent on the electrode materials and their interactions with the proteins and the mediators. In this thesis, the importance of the cleanliness of the system, the adsorption of two types of reaction centers: Wild-type and cysteineless, two mediators: quinone and cytochrome c, and detergents (used to make the reaction center water soluble) on a gold electrode are investigated. It is shown that common cleaning methods such as sonication in a mixture of deionized water and ethyl alcohol, sulfuric acid potential cycling, and piranha solution may not be practical and sufficient to remove the reaction centers and mediators from the electrodes and the container. Additionally, it is shown that eliminating oxygen can result in the reduction of unwanted parasitic reactions in the cell, which could lower the generated photocurrent and hence the overall efficiency of the cell. Therefore, new methods for cleaning and a new cell design are proposed and used throughout the experiments. Capacitance measurements, using cyclic voltammetry and AC voltammetry techniques, in the absence and the presence of each of the cell analytes suggest that unmodified reaction centers, detergents, and the mediators bind to the surface of the gold electrode irreversibly. Finally, it is shown that cysteineless reaction centers also adsorb irreversibly on the surface of the gold, demonstrating that cysteine S-Au bonding is not the only irreversible binding mechanism.

The macroscale electrochemical theory breaks down with microstructures smaller than the dimensions of the diffusion layer, showing that such electrodes have significant quantitative effects and qualitative advantages. The great advantage of microelectrodes over macroelectrodes is the minimisation of interference, which gives rise to much lower detection limits. Microelectrodes have much reduced ohmic drops and capacitive effects and can be used in the absence of supporting electrolyte. These features have opened a growing interest in the fabrication and application of microelectrodes in various areas. There are different microelectrode geometries, but disc type is the most used. Microelectrode arrays have been proposed as a way of increasing the magnitude of the current (produced for a single microelectrode), while maintaining the advantages of the single microelectrode. Although the inlaid microdisc microelectrode can be considered as one the most popular microelectrode geometry, there is also a need to consider conical recessed, recessed and protruding microdiscs as photolithographic microfabrication techniques often result in non-ideal geometries. It has been proved using surface imaging techniques such as scanning Kelvin nanoprobe (SKN), scanning electron microscopy (SEM) and white light interferometer microscopy that conical recessed electrodes with gradient potential along the recessed walls are formed during standard photolithographic methods for producing microelectrode arrays. Microarrays are ubiquitously used for high-throughput measurements using various signal transduction techniques. Ideally each sensor in a microarray platform should perform optimally to ensure an error free response. In this thesis, a simple method for designing a microelectrode array platform (MEA) is described, allowing a ‘defective’ cluster of sensing arrays to be easily identified. It is possible to extend this concept for multiple analyses on a single chip. Molecular electronic is a promising technology which would be an alternative. The concept of molecular electronics is the use of single molecules or arrays, or layers of molecules for the fabrication of electronic components such as wires, switches, and storage elements. Indeed, functionalised thiol monolayer-based microelectrode array may provide unique possibilities, facilitating electrochemical measurements involving electron transfer via electron tunnelling. The conjugated structure of rigid, linear molecule increases greatly the rate of electron transfer across the monolayer. Charge transfer and self-assembly characteristics of novel fully conjugated molecules molecular wires (synthesised at the Department of Chemistry and Centre for Molecular and Nanoscale Electronics, Durham University) assembled on flat gold electrodes are evaluated using Marcus model of electron-transfer and tunnelling theory. The behaviour of these wires is compared with heptanethiol and dodecanethiol SAMs. A preliminary study for application of self-assembled monolayer of molecular wires in microelectrode arrays for multiple analyses on a single chip has been successfully reached.

PhD
SYNOPSIS OF THIS THESIS The aim of this thesis is to more fully understand and explain the binding mechanism of organic molecules to the Au(111) surface and to explore the conduction of such molecules. It consists of five discreet chapters connected to each other by the central theme of “The Single Molecule Device: Conductance and Binding”. There is a deliberate concentration on azine linkers, in particular those with a 1,10-phenanthroline-type bidentate configuration at each end. This linker unit is called a “molecular alligator clip” and is investigated as an alternative to the thiol linker unit more commonly used. Chapter 1 places the work in the broad context of Molecular Electronics and establishes the need for this research. In Chapter 2 the multiple break-junction technique (using a Scanning Tunnelling Microscope or similar device) was used to investigate the conductance of various molecules with azine linkers. A major finding of those experiments is that solvent interactions are a key factor in the conductance signal of particular molecules. Some solvents interfere with the molecule’s interaction with and attachment to the gold electrodes. One indicator of the degree of this interference is the extent of the enhancement or otherwise of the gold quantized conduction peak at 1.0 G0. Below 1.0 G0 a broad range for which the molecule enhances conduction indicates that solvent interactions contribute to a variety of structures which could bridge the electrodes, each with their own specific conductance value. The use of histograms with a Log10 scale for conductance proved useful for observing broad range features. vi Another factor which affects the conductance signal is the geometric alignment of the molecule (or the molecule-solvent structure) to the gold electrode, and the molecular alignment is explored in Chapters 3 for 1,10-phenanthroline (PHEN) and Chapter 4 for thiols. In Chapter 3 STM images, electrochemistry, and Density Functional Theory (DFT) are used to determine 1,10-phenanthroline (PHEN) structures on the Au(111) surface. It is established that PHEN binds in two modes, a physisorbed state and a chemisorbed state. The chemisorbed state is more stable and involves the extraction of gold from the bulk to form adatom-PHEN entities which are highly mobile on the gold surface. Surface pitting is viewed as evidential of the formation of the adatom-molecule entities. DFT calculations in this chapter were performed by Ante Bilic and Jeffery Reimers. The conclusions to Chapter 3 implicate the adatom as a binding mode of thiols to gold and this is explored in Chapter 4 by a timely review of nascent research in the field. The adatom motif is identified as the major binding structure for thiol terminated molecules to gold, using the explanation of surface pitting in Chapter 3 as major evidence and substantiated by emergent literature, both experimental and theoretical. Furthermore, the effect of this binding mode on conductance is explored and structures relevant to the break-junction experiment of Chapter 2 are identified and their conductance values compared. Finally, as a result of researching extensive reports of molecular conductance values, and having attempted the same, a simple method for predicting the conductance of single molecules is presented based upon the tunneling conductance formula.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico
The aim of this work is to study the surface modification of gold electrode with the trans-[Ru(NH3)4(tina)(SO4)]+ (Au/trans-[Ru(NH3)4(tina)(SO4)]+) and trans-[Fe(cyclam)(NCS)2]+ (Au/trans-[Fe(cyclam)(NCS)2]+) complexes ion, emplyoing the electrodeposition and self-assembled monolayer techniques, respectively; and evaluate the potentiality of these modified electrodes as electrochemical sensors for detection and quantification of NO. Cyclic voltammetry and electrochemical quartz crystal microbalance results suggest that the deposition of trans-[Ru(NH3)4(tina)(SO4)]+ complex ion on the gold surface. Cyclic voltammetry and surface enhanced raman spectroscopy results confirm the modification of gold electrode surface by the trans-[Fe(cyclam)(NCS)2]+ complex ion. Peak current (Ip) observed in cyclic voltammograms for the oxidation of NO on the modified electrodes were higher than that observed for the unmodified gold electrode, and the modified electrode Au/trans-[Fe(cyclam)(NCS)2]+ showed the highest Ip for the oxidation of NO. The values of detection limit and quantification limit obtained for the electrode Au/trans-[Ru(NH3)4(tina)(SO4)]+ were 7.73 x 10-8 mol L-1 and 2.58 x 10-7 mol L-1, and for the electrode Au/trans-[Fe(cyclam)(NCS)2]+ were 5.15 x 10-8 mol L-1 and 1.72 x 10-7 mol L-1, respectively, being this values smaller by an order of magnitude as the same obtained for the unmodified gold electrode. Computational simulations suggest that the increase in Ip oxidation of NO on the electrode Au/trans-[Fe(cyclam)(NCS)2]+ is due to the interaction energy between molecules of NO and the complex trans-[Fe(cyclam)(NCS)2]+, adsorbed on the gold surface, to be stronger than the energy of interaction of NO with the gold surface. The dopamine and serotonin molecules and the nitrite ion interfere in electrochemical detection of NO and dopamine and serotonin showed greater interference in the detection of NO in relation to the nitrite ion. The electrode Au/trans-[Fe(cyclam)(NCS)2]+ showed the greatest stability when compared to the electrode Au/trans-[Ru(NH3)4(tina)(SO4)]+. The results obtained in this work showed the potentiality of modified electrodes as sensors for deteccion and quantification of NO, among which stands out the electrode Au/trans-[Fe(cyclam)(NCS)2]+ due to the further intensification of the signal current for the oxidation of NO and provided greater stability.
O objetivo deste trabalho à estudar a modificaÃÃo da superfÃcie do eletrodo de ouro com os Ãons complexos trans-[Ru(NH3)4(tina)(SO4)]+ (Au/trans-[Ru(NH3)4(tina)(SO4)]+) e trans-[Fe(cyclam)(NCS)2]+ (Au/trans-[Fe(cyclam)(NCS)2]+), empregando as tÃcnicas de eletrodeposiÃÃo e formaÃÃo de camadas auto-organizadas, respectivamente; e avaliar a potencialidade destes eletrodos modificados como sensores eletroquÃmicos para detecÃÃo e quantificaÃÃo de NO. Os resultados de voltametria cÃclica e de microbalanÃa eletroquÃmica a cristal de quartzo sugerem a deposiÃÃo do Ãon complexo trans-[Ru(NH3)4(tina)(SO4)]+ sobre a superfÃcie de ouro. Os resultados de voltametria cÃclica e de espalhamento raman amplificado por superfÃcie comprovam a modificaÃÃo da superfÃcie do eletrodo de ouro pelo Ãon complexo trans-[Fe(cyclam)(NCS)2]+. As correntes de pico (Ip) observadas nos voltamogramas cÃclicos para a oxidaÃÃo do NO sobre os eletrodos modificados foram maiores que as observadas para o eletrodo de ouro sem modificaÃÃo, sendo que o eletrodo modificado Au/trans-[Fe(cyclam)(NCS)2]+ apresentou a maior Ip para a oxidaÃÃo de NO. Os valores de limite de detecÃÃo e de quantificaÃÃo obtidos para o eletrodo Au/trans-[Ru(NH3)4(tina)(SO4)]+ foram de 7,73 x 10-8 mol L-1 e 2,58 x 10-7 mol L-1, e para o eletrodo Au/trans-[Fe(cyclam)(NCS)2]+ foram de 5,15 x 10-8 mol L-1 e 1,72 x 10-7 mol L-1, respectivamente, sendo estes valores menores em uma ordem de grandeza que os mesmos obtidos para o eletrodo de ouro nÃo modificado. As simulaÃÃes computacionais sugerem que o aumento de Ip da oxidaÃÃo de NO sob o eletrodo Au/trans-[Fe(cyclam)(NCS)2]+ à devido à energia de interaÃÃo entre as molÃculas de NO e o complexo trans-[Fe(cyclam)(NCS)2]+, adsorvido na superfÃcie de ouro, ser mais forte que a energia de interaÃÃo do NO com a superfÃcie de ouro. As molÃculas dopamina e serotonina e o Ãon nitrito interferem na detecÃÃo eletroquÃmica de NO e a dopamina e a serotonina apresentaram maior interferÃncia na detecÃÃo de NO em relaÃÃo ao Ãon nitrito. O eletrodo Au/trans-[Fe(cyclam)(NCS)2]+ apresentou maior estabilidade quando comparado ao eletrodo Au/trans-[Ru(NH3)4(tina)(SO4)]+. Os resultados obtidos neste trabalho demonstram a potencialidade dos eletrodos modificados como sensores para detecÃÃo e quantificaÃÃo de NO, dentre os quais se destaca o eletrodo Au/trans-[Fe(cyclam)(NCS)2]+, devido à maior intensificaÃÃo no sinal de corrente para a oxidaÃÃo de NO e a maior estabilidade apresentada.

Nanoparticle-functionalized electrodes have attracted attention in areas such as energy production and storage, sensing, and electrosynthesis. The electrochemical properties of these electrodes depend upon the nanoparticle properties, e.g., core size, core morphology, surface chemistry, as well as the structure of the nanoparticle/electrode interface, including the coverage on the electrode surface, choice of electrode support, and the interface between the nanoparticle and the electrode support. Traditionally used methods of producing nanoparticle-functionalized electrodes lack sufficient control over many of these variables, particularly the nanoparticle/electrode interface. Tethering nanoparticles to electrodes with molecular linkers is a strategy to fabricate nanoparticle-functionalized electrodes that provides enhanced control over the nanoparticle/electrode structure. However, many existing tethering methods are done on catalytically active electrode supports, which makes isolating the electrochemical activity of the nanoparticle challenging. Furthermore, previous work has focused on larger nanoparticles, yet smaller nanoparticles with core diameters less than 2.5 nm are of interest due to their unique structural and electronic properties. This dissertation addresses both of these gaps, exploring small nanoparticle electrocatalysts that are molecularly tethered to catalytically inert electrodes. This dissertation first reviews and compares the methods of fabricating nanoparticle-functionalized electrodes with a defined molecular interface in the context of relevant attributes for electrochemical applications. Next, a new platform approach to bind small gold nanoparticles to catalytically inert boron doped diamond electrodes through a defined molecular interface is described, and the influence of the nanoparticle/electrode interface on the electron transfer properties of these materials is evaluated. The next two studies build upon this platform to evaluate molecularly tethered nanoparticles as oxygen electroreduction catalysts. The first of these two describes the systematic study of atomically precise small gold clusters, highlighting the influence of atomic level differences in the core size and the electrode support material on the catalytic properties. The second study extends the platform approach to study small bimetallic silver-gold nanoparticles produced on the electrode surface and highlights the influence of the structural arrangement of the metals on the catalytic activity. Finally, future opportunities for the field of molecularly tethered nanoparticle-functionalized electrodes are discussed. This dissertation includes previously published and unpublished co-authored material.
2019-01-27

Hydrogen evolution via proton reduction occurs at a high rate at the surface of Pt than at Au electrodes. Using cyclic voltammetry, chemically modified nanometer-sized Au electrodes, prepared by the Laser-Assisted Puller Method, were employed to examine current amplification by electrocalysis at Pt nanoparticles adsorbed on the modified Au electrode surfaces. The electrodes were modified with Self-Assembled Monolayers (SAMs) of cysteamine and soaked in Pt colloid solutions overnight. Monitoring the decrements of the characteristic steady-state catalytic current for proton reduction indicated that aggregates of Pt nanoparticles are adsorbed on the cysteamine monolayers and desorb from them particle by particle. The results also indicate that some particles are strongly attached to the modified electrode surface and do not deplete even after thorough rinsing.

This work reports the use of the vibrating gold microwire electrode, with new methods developed for the speciation of Zn, Cu, Mn and As at natural levels in waters of neutral pH. Trace metals and metalloids can be distributed as different species in the environment, which can control mobility, toxicity and bioavailability and in turn depends on many complex factors. Analysis of this distribution (speciation) can provide an understanding of the relationship between such elements and their relationship with organisms in marine environments and humans through contaminated drinking water supplies. Such speciation can be analysed using a vibrating gold microwire electrode (VGME), which is easily prepared and maintained at minimal cost. High sensitivity is found for trace metals: Mn; Cu and Zn; and the metalloid As, resulting from a very low diffusion layer (~0.8 urn for a Sum gold wire) means that they can be measured at trace levels in natural waters. This combined with the VGME's portability, reliability and stability for long term measurement (repeated measurements over several days) and its capability to distinguish between distinct forms ofthe above trace elements mean that speciation methods could be successfully developed and validated in natural waters, with no, or minimal sample preparation. Such methods made it possible to analyse speciation on-site, which decreases the potential problems inherent in maintaining sample speciation during storage. Contamination of groundwater with As is a major health risk through contamination of drinking and irrigation water supplies. In geochemically reducing conditions As is mostly present as ASIII, which is why a method that uses cathodic stripping voltammetry (CSV) to determine reactive AS"I was developed. The ASIII is detected after adsorptive deposition of As(OHho, followed by a potential scan to measure the reduction current from AsIII to Aso. The method is suitable for waters of pH 7-12. The CSV method was successfully applied to groundwaters from Severn Trent, UK, however speciation using this method is severely hampered by high levels of iron and manganese. Experiments showed that the interference is eliminated by addition of EDTA, making it possible to determine the arsenic speciation on-site by CSV in West Bengal, India. The VGME is also used to detect nanomolar levels of dissolved Mn by anodic stripping chronopotentiometry (ASC) and sub-nanomolar levels of dissolved Zn by anodic stripping voltammetry (ASV) in neutral pH seawater. The limits of detection for Mn (1.4 nM) and for Zn (0.3 nM) in seawater with a 300 s plating time, are better than achieved using other non-mercury based electrodes and nearly as good as a mercury film electrode for Zn. Deposition of Mn at the VGME was further utilised to catalyse the reduction of Asv to ASIII, enabling for the first time the direct electrochemical determination of Asv in natural waters of neutral pH including seawater by ASV using a manganese coated gold microwire electrode. Direct electrochemical determination of Asv in neutral pH waters is impossible due to its electro-inactivity. Therefore Mn is added to excess (~1 JlM Mn) to the water leading to a Mn coating during the deposition of Asv on the electrode, when depositing at -1.3 V. The detection limit was 0.2 nM Asv using a deposition time of 180 s. Speciation of Cu is determined without the need for sample preparation, using scanned stripping techniques for the first time at natural levels in seawater. A desorption potential (-1.2 V) and a conditioning interval between scans make the VG ME suitable for on-site and potentially in-situ copper speciation. The resulting pseudopolarograms are analysed using an experimentally constructed 'chelate scale' to determine the strength of copper ligand interactions in real seawater samples.

In this project a new type of metal oxide semiconductor (MOS) sensor for biosensing was investigated. With the use of a porous gold film as aninternal reference electrode, measurements of pH were performed in liquid. This new approach for liquid measurements demands new methods andstudies to increase the conductivity and adhesion in liquid of the porous gold film. The films have been deposited, either by sputtering orevaporation. Extensive studies included the investigation of depositions parameters on film structure and investigating the film morphology. Thesurface structure was studied with a scanning electron microscope (SEM). pH measurements were preformed with promising results. The adhesionof the electrode was greatly improved by using grains of titanium underneath the gold film. This new approach could lead to new applications anddevices for MOS sensors and its sensor relatives.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2005.
Includes bibliographical references (p. 87-90).
This work explored the possibility of using the soluble methane monooxygenase (MMO) enzyme, a three-component enzyme which catalyzes the oxygenation of methane and other substrates, to design a methane sensor for use in natural waters. Such a sensor would be useful for monitoring lake biogeochemistry, including the potential for lakes to be a source of methane into the atmosphere. An op amp-based potentiostat was constructed, and a LabVIEW program was written to control the instrument and acquire data digitally. Cyclic voltammetry experiments were conducted with both acetonitrile, a liquid substrate, and the natural substrate methane. With the hydroxylase component of the enzyme (MMOH) adsorbed onto a peptide-modified gold electrode, the amount of charge transferred during a scan depended on both substrate and oxygen concentrations. This concentration dependence did not occur when MMOH was not present. In the case of methane, the kinetic limitations of partitioning between gas and liquid phases may have contributed to experimental scatter. These results raise the possibility that MMOH may be used without the other two components to generate a reproducible, concentration-dependent signal. Signal strength was also dependent on the order in which high- and low-concentration trials were conducted. The hydroxylase may be able to store methane and oxygen in a hydrophobic cavity for later use, an observation that has both ecological and sensor-design implications.
by Janet Duanping Chuang.
S.M.

This thesis presents the results of a spectroelectrochemical investigation into the interactions of two flotation collectors (mercaptobenzothiazole (MBT) and dithiophosphate (DTP)) with gold electrode and nanorods surfaces. The relevant compounds and ligands of these two collectors were characterised and identified by Raman spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Gold nanorods (Au NRs) with average aspect ratio of 4.04 ± 0.08 were synthesised and reacted with MBT and DTP. Gold particle flotation was investigated using controlled potential techniques. Electrochemical techniques have also been used to investigate the open circuit potential (OCP) and controlled potential oxidation of chalcopyrite. The interaction of collectors with gold electrode surfaces was investigated using in situ surface-enhanced Raman scattering (SERS) spectroscopy. The SERS surface for a gold electrode was generated by electrochemically roughening using an oxidation-reduction cycling (ORC).
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Natural Sciences
Science, Environment, Engineering and Technology
Full Text

In-situ optical second harmonic generation (SHG) spectroscopy was used to examine the potential induced surface reconstruction of a Au (110) surface in a solution of 0.01 M HClO$\sb4.$ The SHG rotational anisotropy was measured at different potentials using the fundamental beam (1064 nm) of the Nd:YAG laser. Analysis of the data shows that the overall symmetry of the surface is C$\rm\sb{s}.$ It was also found that the second order nonlinear susceptibility for both the reconstructed and the unreconstructed surface have a large three fold symmetry component. We suggest that the three-fold symmetry source is partly due to the (111) microfacets that are present on the (110) surface.

Neste trabalho relata-se pela primeira vez a determinação de adenosina por um biossensor baseado em tirosinase. O biossensor foi desenvolvido mediante a modificação de um eletrodo de carbono impresso (SPE) com nanopartículas de ouro (AuNPs), tirosinase (Tyr) e Nafion, denominado biossensor Nafion/Tyr/AuNPs/SPE. As AuNPs sintetizadas possuem diâmetro médio de 15,0 ± 1,1 nm e sua função é melhorar a via de condução de elétrons entre a enzima e o eletrodo. Utilizou-se o aprisionamento com filme Nafion® para evitar a lixiviação enzimática da superfície do eletrodo. A tirosinase imobilizada apresentou boa atividade frente ao substrato catecol. Verificou-se que a adenosina atua como um inibidor do tipo não-competitivo. O biossensor é estável durante pelo menos 45 dias. Além disso, foi realizada a eletro-oxidação da adenosina para sua determinação. O biossensor apresenta sensibilidade superior em comparação com SPE, AuNPs/SPE e Nafion/AuNPs/SPE. As curvas de calibração revelaram duas faixas lineares para as concentrações de adenosina, de 1,0 × 10-5 mol L-1 até 5,0 × 10-5 mol L-1 e entre 6,0 × 10-5 mol L-1 e 1,2 × 10-4 mol L -1. O limite de detecção (3 × (desvio padrão + média dos brancos)/coeficiente angular da curva) foi de 7,0 × 10-7 mol L-1.
In this work we report for the first time the determination of adenosine by a biosensor based on tyrosinase. The biosensor was developed by modifying a screen-printed carbon electrode (SPE) with gold nanoparticles (AuNPs), tyrosinase (Tyr) and Nafion, denoted as Nafion/Tyr/AuNPs/SPE biosensor. The synthesized AuNPs have a mean diameter of 15.0 ± 1.1 nm and their function is to improve the electron conduction pathway between the enzyme and the electrode. The entrapment with Nafion® film was selected to prevent the enzyme lixiviation from the electrode surface. Immobilized tyrosinase showed good activity with the catechol substrate. It was found that adenosine acts as a non-competitive type inhibitor. The biosensor is stable for at least 45 days. In addition, the electro-oxidation of adenosine was performed for its determination. The biosensor has superior sensitivity compared to SPE, AuNPs/SPE and Nafion/AuNPs/SPE. Calibration curves revealed two linear ranges for adenosine concentrations of 1,010-5 mol L-1 up to 5,010-5 mol L-1 and from 6,010-5 mol L-1 to 1,210-4 mol L-1. The detection limit (3 × (standard deviation + mean of blanks)/slope of the curve) was 7,010-7 mol L-1.

Electrochemical method has been used to study the interaction between DNA and the compound N-(3',6'-dihydroxy-3-oxospiro[isobenzofuran-1(3H),9'-[9H]xanthen]-5-yl)-N'-(2-imidazoyl)urea having anticancer properties. A DNA modified nanometer-sized gold electrode was prepared by surface modification of a bare gold electrode using cysteamine. These electrodes have been characterized using electrochemical techniques and were used to study the interaction between DNA and the compound. Our results showed an increase in the adsorption peak current and a negative shift of E1/2 in the oxidation of ferrocyanide on cysteamine and DNA modified electrodes. For the interaction between the DNA and the compound having anticancer properties, a decrease in peak current of the oxidation of ferrocyanide was observed. The decrease in peak current is attributed to the shielding of the electroactive species by the compound intercalated to the DNA from reaching the electrode surface. Therefore, only few of the electroactive species are able to reach the electrode surface.

Philosophiae Doctor - PhD
In this work, DNA aptamer biosensor systems were developed for the detection of l7p-estradiol - an estrogeneous endocrine disrupting chemical (EDC). Endocrine disrupting chemicals are group of compounds that impact negatively on the endocrine system of humans and wildlife. High concentrations of l7p-estradiol in water or food chain disrupts the physiology of the endocrine system of various animal species, leading to feminisation in fish and stimulates the proliferation of cancer cells in humans. Aptasensor systems for the determination of l7pestradiol were prepared with three immobilization platforms: (i) poly(3,4- ethylenedioxythiophene) {PEDOT} doped with gold nanoparticles (AuNPs) to form PEDOTIAuNPs polymeric nanocomposite, (ii) generation 1 poly(propylene thiophenoimine)-copoly( 3 ,4-ethy lenedioxythiophene) dendritic star copolymer (G 1PPT -co-PEDOT), and (iii) generation 2 poly (propylene thiophenoimine)-co-poly(3,4-ethylenedioxythiophene) dendritic star copolymer (G2PPT-co-PEDOT). The morphological properties of the sensor platforms were interrogated by scanning emission microscopy (SEM) and atomic force microscopy (AFM), while their spectroscopic characteristics were studied by Fourier transform infra red spectroscopy (FTIR) and fluorescence spectroscopy. The electrochemical behaviour of the platforms and the aptasensors were studied by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and square wave voltammetry (SWV). The DNA aptamer developed for detecting 17~-estradiol and which was used in the fabrication of all aptamer biosensors in this study is a 76-mer biotinylated aptamer (5'-BiotinGCTTCCAGCTTATTGAATTACACGCAGAGG TAGCGGCTCTGCGCATTCAATGCTGCGCGCTGAAGCGCGGAAGC-3'). AulPEDOTIAuNPslAptamer (platform 1) was obtained by covalently attaching streptavidin to the polymeric nanocomposite platform using carbodiimide chemistry and the aptamer immobilized via streptavidin-biotin interaction. The electrochemical signal generated from the aptamer-target molecule interaction was monitored electrochemically using cyclic voltammetry and square wave voltammetry in the presence of [Fe(CN)6J 3-/4- as a redox probe. The signal current observed was inversely proportional to the concentration of 17Bestradiol. The aptasensor demonstrated specificity toward 17~-estradiol. The detectable concentration range of the 17B estradiol was 0.01 nM-O .09 nM with a detection limit of 3.2 pM. The 76-mer biotinylated aptamer for 17~-estradiol was incorporated into a generation 1 poly(propylenethiophenoimine )-co-poly(3 ,4-ethylenedioxythiophene) dendritic star copolymer modified Au electrode via biotin-avidin interaction (platform 2). The Bode plot shows that the charge transfer dynamics of the nanoelectrode can be frequency modulated while the AulG 1PPTco- PEDOT nanoelectrode exhibited greater semi-conductor behavior (higher phase angle value) than AulG 1PPT due to the incorporation of charged functionalized dendrimer at low frequencies (100 mHz). The biosensor response to 17~-estradiol was based on the decrease in the SWV current as the EDC binds to the ssDNA aptamer on the biosensor. The dynamic linear range of the sensor was 0.01-0.07 nM with a detection limit of7.27 pM. Synthesis of electro synthetic generation G2PPT-co-PEDOT (platform 3) was performed by copolymerization of PEDOT with G2PPT dendrimer modified electrode immersed in a solution of 0.1 M LiCI04 containing 0.1 M EDOT monomer and 0.1 M sodium dodecyl sulphate (SDS) for ten (10) cycles. The electrochemical behaviour of the dendritic star copolymer was investigated with CV and EIS in LiCI04 and phosphate buffer solutions. The results show that the electrochemical deposition of G2PPT-co-PEDOT on gold electrode decreased the electrochemical charge transfer resistance when compared to AuiPEDOTILiCI04 and AuiLiCI04 interfaces. Bode impedimetric analysis indicates that G2PPT-co-PEDOT is a semiconductor. The fabrication of two novel aptasensors (based on platforms 2 and 3) simultaneously on a screen printed micro array electrode of 96-well multichannel electrochemical robotic sensor testing system for the detection of endocrine disrupting l7~-estradiol, was also carried out. The aptasensors responses to l7~-estradiol, based on the decrease in the SWV current, were evaluated.

Ce travail porte sur l’étude électrochimique et par microscopie de fluorescence in situ de l’auto-assemblage, sur électrode d’or, de monocouches d’aptamères peptidiques de la protéine p53 en vue de la détection de la protéine MDM2. L’utilisation de nouvelles sondes de reconnaissance moléculaire telles que les aptamères peptidiques a été considérée en tant qu’alternative à l’utilisation d’anticorps. Les aptamères peptidiques sont des séquences synthétiques de peptide se liant à la protéine cible avec une affinité et une spécificité élevées. La première partie de ce travail porte sur l’étude électrochimique de l’interface modifiée résultant de diverses procédures d’immobilisation. Des mesures en présence du marqueur rédox [Ru(NH3)6]3+ ont démontré l’immobilisation de la sonde peptidique à la surface d’or et ont permis l’évaluation relative de la densité de sondes adsorbées à la surface respectivement à la méthode d’immobilisation considérée. Par ailleurs, des mesures en présence du couple rédox [Fe(CN)6]3-/4- ont mis en évidence une inhibition drastique du transfert d’électron dans le cas de monocouches composées exclusivement du peptide. Dans un second temps, nous nous sommes intéressés à la détection de la protéine MDM2. Trois interfaces modifiées ont été envisagées soit deux monocouches mixtes de peptide et de 4-mercaptobutan-1-ol, ce dernier jouant le rôle de diluant, adsorbés en une ou en deux étape(s), et une monocouche uniquement composée de peptide. L’utilisation de la spectroscopie d’impédance électrochimique en présence du couple rédox [Fe(CN)6]3-/4- comme méthode de détection a mis en exergue la pertinence de cette dernière interface pour la détection. En effet, l’inhibition du transfert d’électron préalablement identifiée est fortement amoindrie suite à l’interaction avec la protéine cible. Une gamme de détection s’étendant de ~1 à 60 ng mL-1 et une limite de détection de 0,69 ng mL-1 ont été obtenues. Cette performance est comparable à celle des kits ELISA commerciaux. La fiabilité et la spécificité de la réponse ont été vérifiées par le biais de contrôles négatifs sur trois protéines, en l’occurrence le fibrinogène, le cytochrome c et l’albumine de sérum bovin, et validées par des mesures complémentaires de microbalance à cristal de quartz.La troisième partie de ce travail est consacrée à l’étude, par microscopie de fluorescence in situ, de l’organisation de la monocouche résultant des trois procédures d’auto-assemblage précitées. Ces mesures ont permis la mise en évidence d’une distribution hétérogène de la densité en sondes, et plus particulièrement la présence d’agrégats. Ceux-ci ne peuvent être désorbés de la surface par l’application de potentiels même très négatifs (-1,450 V vs Ag
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

This paper describes the development of an electrochemical sensor glassy carbon modified with gold nanoparticles and a film of multiâwalled carbon nanotube and cobalt phthalocyanine (CoPc-fMWCNTs/AuNp/GCE) for the determination of diethylstilbestrol hormone (DES) in water samples and meat, using a square wave technique voltammetry. (SWV). The electrolyte used was Britton-Robinson buffer (BR) 0.04 mol L-1 pH 10.0. Initially it was studied the electrode configuration to be used for the development work, after the optimization of solution pH, study scan speed to evaluate the charge transfer kinetics in the redox process of the DES, the optimized parameters for SWV, the analytical curve, and finally, applying the methodology developed. The optimized parameters for SWV were f = 5 sâ1, a = 50 mV and ΔEs=1 mV. The CoPc-fMWCNTs/AuNp/GCE was ready to be used for the application since all conditions were optimized. Analytical curves were obtained in the concentration ranged from 7.9365 Ã 10−7 â 5.6604 Ã 10−6 mol Lâ1 (R = 0.9996) and there were obtained limits of detection (LOD) and quantification (LOQ) of 1.9910 x 10â7 mol Lâ1and 6.6367 x 10â7 mol Lâ1, respectively, being comparable to those reported in the literature. The repeatability and reproducibility of the proposed procedure were evaluated. The relative standard deviation (RSD) were 4.33% and 3.49%, respectively, indicating the precision of the assay. The recovery percentage was 98.56% for the water sample and 94.05% for beef sample (RSD of 0.40 and 1.55% respectively). The modified electrode has developed sensitivity, reproducibility and repeatability appropriate and consistent LOD and LOQ values with those reported in the literature. Moreover, the results obtained by the use of CoPc-fMWCNTs/AuNp/GCE proved very efficient as the detection and DES recovery, being thus a promising device in the detection and quantification of DES in water samples and food.
O presente trabalho descreve o desenvolvimento de um sensor eletroquÃmico de carbono vÃtreo modificado com nanopartÃculas de ouro, nanotubos de carbono de paredes mÃltiplas funcionalizados e ftalocianina de cobalto (CV/NpAu/NTCPMf-FcCo) para a determinaÃÃo do hormÃnio dietilestilbestrol (DES) em amostras de Ãgua e carne, utilizando a tÃcnica de voltametria de onda quadrada (VOQ). O eletrÃlito empregado foi tampÃo BrittonâRobinson (BR) 0,04 mol Lâ1 pH 10,0. Inicialmente estudou-se a configuraÃÃo do eletrodo a ser utilizado para o desenvolvimento do trabalho, depois a otimizaÃÃo do pH do meio, estudo da velocidade de varredura para avaliar a cinÃtica de transferÃncia de carga no processo redox do DES, otimizaÃÃo dos parÃmetros da VOQ, construÃÃo da curva analÃtica e por fim, a aplicaÃÃo da metodologia desenvolvida. Os parÃmetros otimizados para a VOQ foram: f = 5 sâ1, a = 50 mV e ΔEs = 1 mV. De posse de todas as condiÃÃes otimizadas para aplicaÃÃo do CV/NpAu/NTCPMf-FcCo, curvas analÃticas foram obtidas no intervalo de concentraÃÃo de 7,9365 à 10−7 â 5,6604 à 10−6 mol Lâ1 (R = 0,9996) e os limites de detecÃÃo (LD) e de quantificaÃÃo (LQ) calculados foram 1,9910 x 10â7 mol Lâ1 e 6,6367 x 10â7 mol Lâ1, respectivamente, sendo comparÃveis aos citados na literatura. A repetibilidade e a reprodutibilidade do procedimento proposto foram avaliadas. Os valores de desvio padrÃo relativo (DPR) obtidos foram 4,33% e 3,49%, respectivamente, evidenciando a precisÃo da metodologia. O percentual de recuperaÃÃo foi de 98,56% para amostra de Ãgua e 94,05% para amostra de carne bovina (DPR de 0,40 e 1,55% respectivamente). O eletrodo modificado desenvolvido apresentou sensibilidade, reprodutibilidade e repetibilidade adequados, bem como valores de LD e LQ concordantes com os relatados na literatura. Os resultados obtidos pelo emprego do CV/NpAu/NTCPMf-FcCo se mostraram muito eficientes quanto à detecÃÃo e recuperaÃÃo de DES, mostrando-se, desse modo, um dispositivo promissor na detecÃÃo e na quantificaÃÃo de DES em amostras de Ãgua e alimentos.

In this thesis, I present the electrochemical studies of three dendrimeric polypropylene imine (PPI) nanomaterials and their applications as a platform in the development of a novel label free DNA nanobiosensor based on electrochemical impedance spectroscopy. Cyclic voltammetry (CV), differentia pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivities of the nanomaterials on glassy carbon electrode (GCE) as the working electrode.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2018-09-28T14:09:15Z No. of bitstreams: 2 Dissertação - Vinicius Carlos Costa Silva - 2018.pdf: 2032136 bytes, checksum: d25ea59456e929f9d6d4588e5f39838d (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)
Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2018-09-28T14:18:01Z (GMT) No. of bitstreams: 2 Dissertação - Vinicius Carlos Costa Silva - 2018.pdf: 2032136 bytes, checksum: d25ea59456e929f9d6d4588e5f39838d (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)
Made available in DSpace on 2018-09-28T14:18:01Z (GMT). No. of bitstreams: 2 Dissertação - Vinicius Carlos Costa Silva - 2018.pdf: 2032136 bytes, checksum: d25ea59456e929f9d6d4588e5f39838d (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2018-08-31
Electroanalytical techniques are extensively studied for the quantification of species of biological and pharmacological interest. In general, they present high sensitivity and low costs, which, combined with the possibility of miniaturization and real-time analysis, has generated increasing attention in recent times. This work describes an electroanalytical dopamine research system using voltametric techniques through the application of a modified carbon electrodeposite (EPCM) carbon paste electrode. The electrochemical measurements were performed in a potentiostat using a three electrode system, using a gold electrode as working electrode (EPCM), AgCl electrode as reference and platinum wire as electrode. The kinetics of dopamine oxidation was investigated by cyclic voltammetry and by square wave voltammetry using EPCM in dopamine standard solution, without and with sodium metabisulfite (additive present in the drug). By cyclic voltammetry, different scanning velocities were used as a methodology to identify the type of kinetic control, whereas square wave voltammetry was used, with the use of factorial design, to investigate how the gold electrodeposing variables influence the oxidation of DA. he effect of the pH of the medium was also investigated, using phosphate buffer at different pH. Furthermore, under optimized conditions the effect of various concentrations of DA was investigated in order to obtain an analytical curve. The results show by means of measurements by cyclic voltammetry in solutions of DA with and without metabisulfite, that the anodic current of the DA increases from potentials more positive than +0,225 V, with a peak at +0,320. Factorial design observed that sodium metabisulfite significantly decreased the peak current for oxidation of DA. In quadra wave voltammograms for EPCM in phosphate buffer solutions pH 7 containing dopamine and sodium metabisulfite, it is observed that the peak oxidation of dopamine occurs at +0.195 V, while the oxidation of the metabisulfite occurs at approximately +0.834 V. In the study of the pH effect it is verified that an increase of the current occurs when the pH value is above 6.0, while the oxidation potential of the dopamine shifts to more negative values from pH 2, having a sigmoid relation. In the parameter effect of the concentration it was possible to conclude that using this type of modification (gold electrodeposits) showed an improvement in the peak currents when compared to the unmodified electrode. The linearity ranges obtained using EPCM were 3.17 × 10-5 - 1.06 × 10-4, but it was not possible to obtain an ideal calibration curve for the determination of dopamine.
As técnicas eletroanalíticas são amplamente estudadas para quantificação de espécies de interesse biológico e farmacológico. De modo geral, apresentam alta sensibilidade e baixos custos, o que, aliado à possibilidade de miniaturização e análise em tempo real, tem gerado atenção crescente nos últimos tempos. Este trabalho descreve um sistema eletroanalítico de investigação de dopamina utilizando técnicas voltametricas através da apliacação de um eletrodo de pasta de carbono modificado com eletrodepositos de ouro (EPCM). As medidas eletroquímicas foram realizadas em um potenciostato utilizando um sistema de três eletrodos, empregando eletrodo de ouro como eletrodo de trabalho (EPCM), eletrodo de AgCl como referência e fio de platina como contra eletrodo. A cinética de oxidação de dopamina foi investigada por voltametria cíclica e por voltametria de onda quadrada utilizando o EPCM em solução padrão de dopamina, sem e com metabissulfito de sódio (aditivo presente no medicamento). Por voltametria cíclica foi utilizada diferentes velocidades de varredura como metodologia para identificar o tipo de controle cinético, enquanto que a voltametria de onda quadrada foi empregada, com uso de planejamento fatorial, para investigar como as variáveis de eletrodeposição de ouro influenciam sobre a oxidação de DA. Também foi investigado o efeito do pH do meio, utilizando-se tampão fosfato a diferentes pH. Além disso, sob condições otimizadas foi investigado o efeito de várias concentrações de DA, com a finalidade de se obter uma curva analítica. Os resultados mostram através das medidas por voltametria cíclica em soluções de DA com e sem metabissufito, que a corrente anódica da DA aumenta a partir de potenciais mais positivos que +0,225 V, apresentando um pico em +0,320. Diante do planejamento fatorial observou que o metabissulfito de sódio diminui significativamente a corrente de pico para oxidação da DA. Nos voltamogramas de onda quadra para o EPCM nas soluções tampão fosfato pH 7 contendo dopamina e metabissulfito de sódio, observa-se que o pico de oxidação da dopamina ocorre em +0,195 V, enquanto que a oxidação do metabissulfito ocorre em aproximadamente +0,834 V. No estudo do efeito do pH verifica-se que ocorre um aumento da corrente quando o valor de pH está acima de 6,0, enquanto que o potencial de oxidação da dopamina desloca para valores mais negativos desde o pH 2, tendo uma relação sigmoide. No parâmetro efeito da concentração foi possível concluir que utilizando este tipo de modificação (eletrodepósitos de ouro) mostrou uma melhora no aumento das correntes de pico quando comparado com o eletrodo não modificado. As faixas de linearidade obtidas utilizando o EPCM foram de 3,17 × 10-5 – 1,06 × 10-4, porém não foi possível obter uma curva de calibração ideal para a determinação da dopamina.

Aspectos fundamentais das reações de eletrooxidação do glicerol e álcoois similares em ouro foram estudados por meio da comparação com a eletrooxidação de álcoois similares: 1-propanol, 2-propanol, propano-1,2-diol e propano-1,3-diol, além de sorbitol e glicose. Testes eletroquímicos foram feitos em soluções ácida, neutra e alcalina. Também foram realizados testes em meio alcalino com os possíveis subprodutos de oxidação do glicerol: dihidroxiacetona, gliceraldeído, glicerato, hidroxipiruvato, mesoxalato, tartronato, oxalato e formato. Por fim, os produtos de reação foram analisados por FTIR in situ e HPLC. Conforme esperado, o ouro foi praticamente inativo para todos os álcoois nos meios neutro e ácido, e muito ativo no meio alcalino. Entretanto, os dados de RDE mostraram que a formação de alcóxido não é a responsável pela atividade, como era proposto até então. Comparando a eletrooxidação do glicerol com álcoois similares, foi possível notar que a presença de hidroxilas vizinhas na molécula é a propriedade mais importante para render altas densidades de corrente (para a eletrooxidação de álcoois em geral) sobre ouro. Ela facilita a quebra das ligações C-C favorecendo a formação de produtos mais oxidados, conforme observado por FTIR e HPLC. As medidas de FTIR in situ também mostraram que pode haver neutralização e até acidificação nas proximidades do eletrodo em meio alcalino (se a concentração de base não for suficientemente alta), devido à formação de subprodutos ácidos, o que pode levar a uma mudança no mecanismo da reação. Medidas de RDE indicam que é possível controlar a seletividade dos produtos de eletrooxidação de glicerol e outros álcoois sobre ouro pela convecção artificial, entretanto, o controle pelo potencial ou concentração são limitados, conforme constatado pela análise de produtos. Os testes realizados com os subprodutos e análise de produtos permitiram refinar a rota reacional de eletrooxidação do glicerol.
Fundamental aspects of glycerol and similar alcohols electrooxidation reactions on gold were studied by comparing with similar alcohols: 1-propanol, 2-propanol, propane-1,2-diol and propane-1,3-diol, and also sorbitol and glucose. Electrochemical measurements were performed in acidic, neutral and alkaline solutions. Moreover, CV tests were performed in alkaline environment with the main possible glycerol oxidation byproducts: dihydroxyacetone, gyceraldehyde, glycerate, hydroxypyruvate, mesoxalate, tartronate, oxalate and formate. Finally, the reaction products were analyzed by in situ FTIR and HPLC. As expected, gold was practically inactive for all alcohols in acidic and neutral conditions, but highly active in alkaline medium. However, RDE data showed that the alkoxide formation is not the responsible for the high activity, as proposed until now. By comparing the glycerol electrooxidation with the other alcohols, it was possible note that the vicinal hydroxyl groups is the key property to yield the high current densities (for alcohols electrooxidation in a general way) seen on gold. It favors the C-C bonding break, that leads to more oxidized products, as seen by FTIR and HPLC data. In addition, FTIR measurements showed that neutralization and even acidification can occur near to the electrode in alkaline medium (if the base concentration is not high enough), due to the formation of acidic byproducts that can also lead to different reaction mechanism. RDE experiments indicated that it is possible to control the selectivity of glycerol and other alcohols electrooxidation products on gold by artificial convection, but control by the potential or concentration are limited, as shown by products analysis. The CV tests with byproducts and products analysis allowed to refine the glycerol electrooxidation reaction pathways.

U ovom radu su razvijene elektrohemijske metode za određivanje histamina. U svimelektrohemijskim ispitivanjima korišćena je hronopotenciometrija. Istraživanja su obuhvatila optimizaciju uslova elektroanalitičkih tehnika i upoređivanje mehanizama generisanja analitičkog signala primenom različitih radnih elektroda, razvoj odgovarajućeg postupka pripreme uzoraka za analizu i samo određivanje histamina u hrani i piću. Ispitana je mogućnost primene čvrste zlatne elektrode, tankoslojne živine i tankoslojne niklove elektrode za elektrohemijsko određivanje histamina. U slučaju elektrooksidacije histamina, razjašnjeni su mehanizmi generisanja signala na primenjenim elektrodama. Optimizacija uslova elektroanalitičkih tehnika obuhvatila je odabir odgovarajućeg pomoćnog elektrolita i njegove koncentracije, ispitivanje uticaja početnog potencijala i struje oksidacije na analitički signal analita. Pored toga, za svaki elektrohemijski sistem definisana su osetljivost i reproduktivnost, selektivnost, kao i opseg linearnosti. Primenom tankoslojne niklove elektrode uočena je pojava adsorpcionog koncentrovanja analita, te su u slučaju ovog elektrohemijskog sistema ispitani i uticaji vremena adsorpcije i temperature ispitivanog medijuma na analitički signal histamina. Na tankoslojnoj živinoj elektrodi analitički signal se generisao usled direktne oksidacije histamina primenom konstantne struje. Na ostale dve elektrode, pored elektrodnih reakcija odvijale su se i hemijske reakcije, tako da se oksidacija histamina u oba slučaja odigravala po ECE mehanizmu (elektrodna reakcija – hemijska reakcija – elektrodna reakcija). Na čvrstoj zlatnoj elektrodi, generisanje signala je bilo posledica oksidacije histamina elektrogenerisanim hlorom, dok se u slučaju tankoslojne niklove elektrode radilo o kombinovanoj katalitičko‐adsorpcionoj hronopotenciometriji. Tankoslojna živina elektroda je pokazala dobru selektivnost pri koncentracijama aminokiselina i histamina nižim od 5 mg/dm³, dok je pri višim koncentracijama dolazilo do preklapanja analitičkih signala. Ostali elektrohemijski sistemi nisu pokazali odgovarajuću selektivnost. Najveća osteljivost je ostvarena primenom tankoslojne niklove elektrode (LOD = 0,11 mg/dm³), zatim sledi čvrsta zlatna elektroda (LOD = 0,27 mg/dm³) i na kraju tankoslojna živina elektroda (LOD = 1,31 mg/dm³). U okviru definisanja postupka pripreme uzoraka, ispitana je efikasnost različitih ekstrakcionih tehnika i različitih ekstragenasa u pogledu izdvajanja histamina iz uzoraka. Pored toga razvijeni su odgovarajući postupci prečišćavanja ekstrakata primenom preparativnih hromatografskih tehnika, i to na tankom sloju i na stubu adsorbensa. Po definisanju optimalnih uslova elektrohemijskog određivanje histamina, kao i razvijanja postupka pripreme uzoraka, histamin je određen u različitoj hrani i piću.
In this work, the electrochemical methods for the determination of histamine weredeveloped. All electrochemical investigations were carried out by chronopotentiometry. The research included optimization of the experimental parameters of electroanalytical techniques and comparison of the mechanism of the analytical signal generation by using the different working electrodes. Upon the development of sample preparation procedure, histamine was determined in different food and beverages. The possibility of applying solid gold electrodes, thin film mercury electrode and thin film nickel electrode for electrochemical determination of histamine was examined. The mechanisms of histamine electrooxidation on different working electrodes were explained and elaborated. Optimization of the experimental parameters of electroanalytical techniques included the selection of appropriate supporting electrolyte and its concentration, and investigation of the influence of initial potential and oxidation current on histamine analytical signal. Beside this, for each electrochemical system sensitivity and reproducibility, selectivity as well as linearity range were defined. The use of thin nickel film electrode resulted in adsorptive accumulation, and in that case the effects of accumulation time and medium temperature on histamine analytical signal were defined. On thin film mercury electrode, histamine analytical signal was generateddue to direct oxidation of histamine by a constant current. On other two electrodes, electrode reactions were coupled with chemical reaction, and histamine oxidation was by ECE mechanism (electrode reaction – chemical reaction – electrode reaction). On solid gold electrode histamine was oxidized indirectly by electrogenerated chlorine, while in the case of thin film nickel electrode combination of catalytic and adsorptive chronopotentiomety was responsible for signal generation. Thin film mercury electrode showed good selectivity for histamine and amino acids concentrations below 5 mg/dm³, but higher concentrations caused the overlapping of analytical signals. Other electrochemical systems did not show adequate selectivity. The best sensitivity was achived by thin film nickel electrode (LOD = 0.11 mg/dm³),followed by a solid gold electrode (LOD = 0.27 mg/dm³), and by thin film mercury electrode (LOD = 1.31 mg/dm³). In order to define adequate sample preparation procedure, the efficiency of different extraction techniques and different solvents were tested for histamine extraction from the samples. Appropriate procedures for purification of extracts were defined as well, by applying preparative thin layer and column chromatography. After optimization of the electrochemical methods for histamine determination, as well as the procedure of sample preparation, developed methods were applied for histamine determination in various food and beverages.

The interaction of drugs with DNA is a significant feature in pharmacology and plays a vital role in the designing of more efficient and specifically targeted drugs.The concept of hybridization of two bioactive molecules often leads to increased activity due to synergistic effects of anticancer drugs have been studied.Two important pharmacophores: Acridine and thiophene were widely studied as antitumor, antiparasitic and antibacterial agents. We hypothesize that a conjugate comprised two pharmacophores with different mechanisms of antiproliferative action can result in enhanced DNA damage. Electrochemical Studies in aprotic and protic media, electrochemical DNA biosensor at Glassy carbon electrode, electrochemical New Hairpin DNA biosensor at the Gold electrode (SL-DNA/GE), Molecular Modeling and Spectroscopic UV-Vis, were used to determine the damage caused to DNA by six Acridine-thiophene conjugates. In this work, we report the synthesis of six synthetic DNA intercalators based on the acridine linked with thiophene conjugates (7CNAC01, 6CNAC01, 7ESTAC01, 6ESTAC01, ACS6CN, and ASC5CN). We identified the electrochemical behavior of these active redox drugs is strongly influenced by the nature of solvent (DMF and pH=7.2 phosphate buffer media).We recorded redox properties of 7CNAC01, 6CNAC01, 7ESTAC01, and 6ESTAC01 involve adsorption controlled quasi- reversible process and were investigated using differential pulse voltammetry (DPV) at a glassy carbon and Gold electrode. An effective and new electrochemical biosensor based on hairpin DNA (SL-DNA/GE) immobilized and functionalized on the surface of the gold electrode (GE) to detect oxidative Guanine damage was developed. As a result, two kinds of biosensor were tested with reduced acridinethiophene conjugates showing better sensitivity the SL-DNA/GE sensor for the detection of DNA damage using the electrochemical signal of Oxidation of Guanine bases. Also, Molecular docking results showed predominantly hydrophobic interaction, and either high binding constant was recorded for Molecular docking and UV-Vis absorption spectroscopy showing an isosbestic point presence with dsDNA, for 7ESTAC01, 6ESTAC01, ACS6CN, ACS5CN. Our findings indicate that three reduced acridine-thiophene compounds (7CNAC01, 6CNAC01, and ACS5CN) cause direct dsDNA damage and all our six reduced hybrid compounds are causing damage to singled stranded ssDNA. Finally, we proposed for the first time a direct correlation between binding constant (Kb) and half-wave potential (E1/2) for four acridine-thiophene derivates (7ESTAC01, 6ESTAC01, ACS6CN, and ASC5CN). Our results showed a promise sensitive electrochemical SL-DNA/GE sensor for the detection of DNA damage using the electrochemical signal of Oxidation of Guanine bases, to detect DNA-cancer drug interaction.
A interação de drogas com DNA é uma característica significativa na farmacologia e desempenha um papel vital na concepção de drogas mais eficientes e especificamente direcionadas. O conceito de hibridização de duas moléculas bioativas leva ao aumento da atividade devido aos efeitos sinérgicos de drogas híbridas anticâncer com o uso dos farmacóforos importantes: Acridina e Tiofeno. Estes dois sítios ativos foram amplamente estudados como agentes antitumorais, antiparasitários e antibacterianos. Suspeitamos que um conjugado, composto por dois farmacóforos com diferentes mecanismos de ação antiproliferativa, pode resultar em danos ao DNA. Estudos eletroquímicos em meios prótico e aprótico, biossensor de DNA eletroquímico em eletrodo de carbono vítreo, Hairpin DNA em eletrodo de ouro (SL-DNA/GE), modelagem molecular e Espectroscopia UV-Vis foram usados para determinar os danos causados ao DNA por seis conjugados de Acridina-Tiofeno. Neste trabalho, relatamos o estudo de seis intercaladores de DNA com base na acridina ligada a conjugados de tiofeno (7CNAC01, 6CNAC01, 7ESTAC01, 6ESTAC01, ACS6CN e ASC5CN). As propriedades redox da 7CNAC01, 6CNAC01, 7ESTAC01 e 6ESTAC01 envolvem processo quase-reversível com corrente controlada por difusão. As propriedades redox desses compostos foram investigadas usando voltametrias cíclica e de pulso diferencial (VPD) em eletrodo de carbono vítreo e eletrodo de ouro. Foi desenvolvido um novo e eficiente biossensor eletroquímico baseado no Hairpin DNA (SL-DNA/GE) imobilizado e funcionalizado na superfície do eletrodo de ouro para detectar danos oxidativos da guanina através da interação com 7ESTAC01. Os biosensores SL-DNA e dsDNA foram testados com conjugados de acridina-tiofeno reduzidos, apresentando melhor sensibilidade o sensor SLDNA na detecção de danos ao DNA. Além disso, os resultados de modelagem molecular mostraram predominantemente interação hidrofóbica e uma alta constante de ligação. Já os resultados de espectroscopia de absorção no UV-Vis mostraram a presença de ponto isosbéstico com dsDNA, para os conjugados 7ESTAC01, 6ESTAC01, ACS6CN, ACS5CN. Nossos resultados indicaram que três compostos de acridina-tiofeno reduzidos (7CNAC01, 6CNAC01 e ACS5CN) causaram danos direto ao dsDNA, e os seis compostos híbridos reduzidos, causaram danos ao DNA de cadeia simples. Finalmente, propusemos pela primeira vez uma correlação direta entre constante de ligação (Kb) e potencial de meia onda (E1 / 2) para quatro derivados de acridina-tiofeno (7ESTAC01, 6ESTAC01, ACS6CN e ASC5CN). Além disso, o biosensor eletroquímico de SL-DNA/GE mostrou-se bastante sensível para a detecção dos danos causados ao DNA, através da interação entre o DNA e os compostos estudados.

Este trabalho apresenta o desenvolvimento e a aplicação de um método alternativo para determinação de manganês em amostras de cimento e clínquer por voltametria de redissolução catódica por onda quadrada empregando eletrodos de ouro. Após estudos exploratórios acerca do comportamento eletroquímico do manganês no eletrólito suporte H3BO3 0,20 mol L-1 / KCl 0,10 mol L-1 com pH 6,5 e a otimização dos parâmetros operacionais para a voltametria de onda quadrada, foram obtidos excelentes resultados na determinação de manganês nas amostras analisadas. Destacam-se a ótima linearidade, verificada em duas faixas distintas de concentração, e os baixos limites de detecção e quantificação obtidos (3,1 x 10-8 mol L-1 e 9,8 x 10-8 mol L-1, respectivamente), além da concordância entre os resultados obtidos pela técnica eletroanalítica quando comparados aos resultados fornecidos pela espectrometria de absorção atômica de chama (FAAS). Para o tratamento das amostras foi avaliada a eficiência da extração ácida assistida por ultrassom. Foram avaliados ácidos minerais individualmente (HCl, H2SO4 e HClO4 em diferentes concentrações), em mistura ou ainda associados a H2O2. Os melhores resultados foram obtidos utilizando uma solução de HCl 3 mol L-1, que extraiu quantitativamente o manganês nas amostras analisadas. Os resultados obtidos foram concordantes com a metodologia padrão utilizada para a abertura da amostra e posterior análise por espectrometria de absorção atômica de chama, que emprega o aquecimento em chapa e a mesma solução extratora.
This work describes the development and application of a new alternative method for determination of manganese in cement and clinker samples by square wave cathodic stripping voltammetry using gold electrodes. After exploratory studies on the electrochemical behavior of manganese in H3BO3 0.20 mol L-1 / KCl 0.10 mol L-1 supporting electrolyte at pH 6.5 and the optimization of operating parameters for the square wave voltammetry, excellent results were obtained for determination of manganese in the samples analyzed. Most notable are the excellent linearity, verified in two distinct concentration bands and the low limits of detection and quantification obtained (3,1 x 10-8 mol L-1 e 9,8 x 10-8 mol L-1, respectively), in addiction to the concordance between the obtained results by the electroanalytical technique when compared to the provided by the flame atomic absorption spectrometry. For samples treatment were tested the efficiency of the ultrasound-assisted extraction. Were evaluated individually mineral acids (HCl, H2SO4 and HClO4 at different concentrations) in a mixture or associated with H2O2. the best results were obtained using a 3 mol L-1 HCl solution, which extracted manganese quantitatively from the analysed samples, in comparison to the standard method for extraction, targeting a later atomic absorption flame spectrometry analysis, which uses the plate heating and the same extracting solution. The obtained results for the analysed samples agrees with the cement and clinker samples of the used literature

Résumé du travail

L’étude des modifications de surfaces, et plus particulièrement des matériaux d’électrodes est un domaine en plein essor. Les modifications d’électrodes par voie organique ont des applications potentielles dans des domaines aussi variés que l’inhibition de la corrosion, l’électronique moléculaire, l’optoélectronique ou encore les biosenseurs.

Dans ce travail, nous nous sommes intéressés à l’électrode d’Au (111) modifiée par du 2-mercaptobenzimidazole.

Dans un premier temps, l’adsorption du MBI sur électrode d’Au (111) sous contrôle du potentiel a été examinée par des mesures de capacité, de voltampérométrie cyclique, de chronocoulométrie et de spectroscopie SNIFTIR in situ.

Les mesures de capacité révèlent qu’en milieu neutre, la molécule de MBI s’adsorbe en un film compact à des potentiels supérieurs à -0,3 V (vs. ECS). En deçà de cette valeur, le film se dilue progressivement lorsque le potentiel est rendu plus négatif, jusqu’à une valeur de -0,9 V où les molécules de MBI sont totalement désorbées de la surface.

La morphologie des voltampérogrammes subit des variations significatives au cours du temps. Ces changements montrent que l’adsorption du MBI s’accompagne d’une levée de reconstruction de la surface, qui passe d’une structure initiale (√3 x 22) à une structure (1 x 1). Une estimation de la quantité de MBI adsorbée est obtenue par intégration des courbes de densité de courant.

La courbe de densité de charge interfaciale a été extraite des mesures de chronocoulométrie. Cette courbe de densité de charge fournit des informations quant à l’évolution de l’excès superficiel en fonction du potentiel.

La qualité des spectres infrarouges relevés in situ nous a permis d’effectuer des analyses qualitatives et quantitatives. Celles-ci montrent une bonne corrélation avec les résultats électrochimiques et apportent une signature moléculaire du film adsorbé et des espèces issues de sa désorption. Des calculs basés sur la Théorie de la Fonctionnelle de la Densité (DFT) ont permis une bonne interprétation des spectres infrarouges du MBI et de certains de ses dérivés. En outre, nous avons pu déterminer l’orientation des molécules à la surface, et montré que celle-ci varie peu avec le potentiel.

Dans un second temps, nous nous sommes focalisés sur les propriétés de la monocouche auto-assemblée de MBI sur électrode d’Au (111), déterminées par voltampérométrie cyclique et spectroscopie infrarouge in situ. La monocouche est stable lorsque le potentiel est maintenu dans un domaine d’environ 800 mV. La monocouche auto-assemblée de MBI subit un processus de désorption réductive, influencé par le temps d’immersion de l’électrode dans la solution de surfactant ainsi que par le pH du milieu. Deux mécanismes de désorption réductive sont proposés, l’un valable en milieu neutre et basique, l’autre en milieu acide. Les résultats des mesures de spectroscopie infrarouge in situ apportent une preuve moléculaire de la validité des mécanismes proposés sur base des résultats électrochimiques.

Un rapide examen des potentialités de cette monocouche a été réalisé à l’aide de réactions sondes.

/

Abstract

Studies on surface modifications, and particularly of electrode material, are a growing field of interest. Organic modifications of electrode surfaces have potential applications in domains such as corrosion inhibition, molecular electronics, optoelectronics or biosensors.

In the present work, we focussed on the modification of Au(111) electrodes by 2-mercaptobenzimidazole (MBI).

In the first part, the adsorption, under potential control, of the MBI molecule onto the Au(111) electrode was studied by means of capacitance measurements, cyclic voltammetry, chronocoulometry and in-situ SNIFTIR spectroscopy.

Capacitance measurements indicate that in neutral solution, the MBI molecule is adsorbed as a compact film at potentials higher than -0.3 V (vs. SCE). Below this value, the film becomes progressively less dense when the potential is made more negative, until a value of -0.9 V where MBI molecules are totally desorbed from the surface.

The shape of the voltammograms evolves significantly with time. These changes show that a lift of the surface reconstruction occurs concomitantly to the adsorption of MBI. The initial (√3 x 22) reconstructed structure is lifted to the (1 x 1) unreconstructed one. The amount of adsorbed MBI is estimated by integration of the current density curves.

The interfacial charge density curve was obtained by chronocoulometry measurements. This curve provides useful data regarding the evolution of the surface concentration with the potential.

The quality of the infrared spectra obtained in situ allowed us to perform quantitative as well as qualitative analyses of the results. These analyses show a good correlation with the electrochemical results and provide molecular information on the adsorbed layer and on the species formed during the desorption process. Density Functional Theory (DFT) calculations were helpful in the interpretation of the infrared spectra of MBI and some of its derivatives. Additionally, we were able to determine the orientation of the molecules on the surface, and demonstrated that this orientation is slightly affected by the potential.

In the second part of the work, we investigated the properties of the self-assembled monolayer of MBI on Au(111) electrode by cyclic voltammetry and in situ infrared spectroscopy. The monolayer is stable within an 800 mV potential range. The self-assembled monolayer undergoes a reductive desorption process, which is affected by the pH of the medium and by the immersion time of the electrode into the surfactant solution. Two mechanisms were proposed for the reductive desorption, one being valid in neutral and basic media, the other in acidic conditions. The in situ infrared spectroscopic results provide molecular evidences supporting the mechanisms proposed on an electrochemical basis.

An exploratory examination of the potentialities of the monolayer is made by means of electrochemical probe reactions.

Doctorat en sciences, Spécialisation chimie
info:eu-repo/semantics/nonPublished

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-07-14T14:18:26Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese de Doutorado - Ana Carolina M.S. Dias.pdf: 7391913 bytes, checksum: 55ab68bd39f956f754684f4b795a7baa (MD5)
Made available in DSpace on 2016-07-14T14:18:27Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese de Doutorado - Ana Carolina M.S. Dias.pdf: 7391913 bytes, checksum: 55ab68bd39f956f754684f4b795a7baa (MD5) Previous issue date: 2015-05-06
FACEPE
A infecção pelo vírus dengue (DENV) é uma das doenças tropicais mais negligenciadas e de maior importância de saúde pública no mundo. Novos métodos de diagnóstico da doença têm sido estudados através da detecção da proteína NS1 do DENV. O antígeno NS1 é um importante marcador precoce da fase aguda da dengue, secretado em altas concentrações pelo vírus no sangue de pessoas infectadas logo nos primeiros dias, porém, não é muito utilizado na rotina laboratorial para diagnóstico da doença devido ao alto custo dos ensaios. A presente tese descreve o desenvolvimento de duas plataformas sensoras eletroquímicas baseadas em eletrodos impressos (EIs) modificados com nanomateriais para detecção do antígeno NS1 do DENV. Os EIs foram confeccionados utilizando-se a impressão de tinta de carbono sobre o polietileno tereftalato (PET), suporte para impressão dos moldes. Inicialmente, foram estudados os efeitos de nanotubos de carbono e sua contribuição na transferência de elétrons, condutividade e aumento de área eletroativa da plataforma sensora. O estudo foi baseado na incorporação de nanotubos de carbono funcionalizados com grupos carboxílicos à tinta de carbono. Para detecção do NS1, um imunoensaio do tipo “sanduíche” foi realizado, no qual a captura específica do NS1 pôde ser avaliada através das reações redox da enzima peroxidase conjugada ao anticorpo. Uma faixa linear entre 0,04 g/mL e 2 g/mL de NS1 foi obtida, indicando boa performance analítica do imunossensor, com coeficiente de correlação linear de 0,996 (p<0.0001, n=8) e limite de detecção de 0,012 g/mL de NS1. Posteriormente, foi investigada a contribuição de nanopartículas metálicas no desenvolvimento de sensores eletroquímicos livres de marcação. Foram utilizadas nanopartículas de ouro (NPsAu) funcionalizadas com grupos amina para a imobilização covalente de anticorpos. Na síntese das NPsAu, foi utilizado o polietilenoimina como agente redutor e funcionalizante para promover uma ligação amida com o anticorpo anti-NS1. O imunossensor desenvolvido mostrou curva de calibração com faixa de concentração linear entre 0,1 g/mL e 2 g/mL de NS1 (r = 0,995, p<0.0001, n=7) e limite de detecção de 0,03 g/mL de NS1. A contribuição dos nanomateriais para as plataformas sensoras desenvolvidas mostrou-se efetiva na sensibilidade analítica, devido ao aumento de área eletroativa e maior quantidade de anticorpos imobilizados. A aplicação destes nanomateriais nos imunossensores proporciona novas alternativas de diagnóstico para detecção da proteína NS1 do DENV.
Infection by Dengue Virus (DENV) is one of the most neglected tropical diseases and of higher importance of public health worldwide. New methods of diagnosis of the disease have been studied through the detection of NS1 protein of DENV. NS1 antigen is an important early marker of acute dengue infection secreted in high concentrations by the virus in the blood of infected people in first days, however it is not widely used in the laboratory routine for diagnosis of the disease due to high cost of assays. The present thesis describes the development of two electrochemical sensor platforms based on screen-printed electrodes (SPEs) modified with nanomaterials for detection of NS1 antigen of DENV. SPEs were prepared using carbon ink printing on the polyethylene terephthalate (PET), support for molds printing. Initially, the effects of carbon nanotubes and their contribution to the electron transfer, conductivity and increase of electroactive area of the sensor platform were studied. The study was based on the incorporation of carbon nanotubes functionalized with carboxylic groups to the carbon ink. For NS1 detection, a sandwich-type immunoassay was carried out, wherein the specific capture of NS1 may be assessed by redox reactions of peroxidase enzyme conjugated to the antibody. A linear range between 0.04 g/mL and 2 g/mL NS1 was obtained, indicating good analytical performance of the immunosensor, with linear correlation coefficient of 0.996 (p<0.0001, n=8) and limit of detection of 0.012 g/mL NS1. Subsequently, the contribution of metal nanoparticles in the development of label-free electrochemical sensors was investigated. Gold nanoparticles (AuNPs) functionalized with amine groups were used for covalent immobilization of antibodies. In the synthesis of AuNPs, polyethyleneimine was used as a reducing and functionalizing agent to promote an amide bond with anti-NS1 antibody. The developed immunosensor showed calibration curve with linear concentration range between 0.1 g/mL and 2 g/mL NS1 (r = 0.995, p<0.0001, n = 7) and limit of detection of 0.03 g/mL NS1. The contribution of nanomaterials for the sensor platforms developed proved effective in the analytical sensitivity due to the increase of electroactive area and larger amount of immobilized biomolecules. The application of these nanomaterials in immunosensors provides new alternatives of diagnosis for detection of NS1 protein of DENV.

Made available in DSpace on 2017-07-24T19:38:05Z (GMT). No. of bitstreams: 1 Rosana Mossanha.pdf: 1591695 bytes, checksum: aac2e3d256b391dd0e8f113bb72eb620 (MD5) Previous issue date: 2011-03-03
In this work were studied investigated different types of modifiers for the formation of self-assembled monolayers on the gold surface. The monolayers used were formed by different structural arrangements, alkyl chains and functional groups. The thiols groups used were: 3-mercaptopropionic acid (MPA), thiolactic acid (TLA), cystamine (CYS) and 11-mercaptoundecanoic acid. The electroactivity of films of different thiols was assessed by the probe molecule, Fe(CN)63-/4-. It was possible to observe through the cyclic voltammetry technique, the formation and organization of the films, monitoring the behavior of the redox couple. The voltammograms showed a decrease in the faradaic current response with the increase of immersion time of the gold substrate in ethanolic solution of thiols, suggesting that the process of electron transfer occurs through the pinholes of the electrodes surface and tunneling. The monolayers of 3-mercaptopropionic acid (MPA) and thiolactic acid (TLA) had a better coating of the surface in immersion time of 3 hours. While the 11-mercaptopropionic acid (MUA) and cystamine (CYS) needed more time to organize the monolayer, 24 hours, because the MUA is a long chain molecule and CYS because the cleavage of S-S. The size of thiol chain influenced the surface organization, short-chain thiols tend to form monolayers with a considerable amount of defects, leading to a lower coating on the electrode surface. Indeed, the MUA that contains a high number of carbons in the chain showed a higher surface coverage, which caused loss of voltammetric response. The electrode surface roughness and the active area, calculated by the voltammetric data, showed a decrease with the formation of the monolayers on gold surface. Aiming to estimate the amount of molecules immobilized on the surface, it was calculated the superficial excess ) by voltammetric charge obtained from the reductive desorption. The obtained values were of 1.88x10-10 for Au-CYS, 5.03x10-10 to Au-MPA, 1.06x10-8 for Au-MUA and 1.35x10-10 mol.cm-2 for the Au-TLA, demonstrating an almost complete coverage of active sites on the surface. By the electrochemical impedance spectroscopy technique, it was possible to determine the kinetic parameters of the SAMs, which were consistent with those obtained by cyclic voltammetry. Analyzing the performance of sensors for dopamine determination through the VC, it was found that the SAM formed by TLA presented the most satisfactory results regarding the sensitivity and selectivity compared to the analyte DA. Studies at different scan rates for the electrodes, Au-MPA, Au-TLA and Au-CYS in the presence of the analite showed that the anodic peak current linearly increases with the square root of scan rate, indicating that the electron transfer process is controlled by diffusion of species to the electrode surface. Dopamine was quantified by CV and SWV technique, in the linear range from 1.1 to 6.6x10-7 mol L-1 with detection limits of 1,42x10-7 mol L-1 and 4,77x10-8 mol L-1, respectively. Using the technique of VOQ, TLA-Au electrode was able to distinguish between AA and DA, when present in the same solution, with a potential difference of approximately 340 mV.
Neste trabalho foram investigados diferentes tipos de modificadores para a formação de monocamadas auto-organizadas sobre a superfície do ouro. As monocamadas utilizadas foram formadas por diferentes arranjos estruturais, tamanho da cadeia carbônica e grupos funcionais. Os tióis utilizados foram: ácido 3- mercaptopropiônico (MPA), ácido tioláctico (TLA), cistamina (CYS) e o ácido 11-mercaptoundecanóico. A eletroatividade dos filmes dos diferentes tióis foi avaliada pela molécula sonda, Fe(CN)6]3-/4-. Foi possível constatar através da técnica de voltametria cíclica, a formação e a organização dos filmes, monitorando o comportamento do par redox. Os voltamogramas mostraram um decréscimo nas respostas da corrente faradaica com o aumento do tempo de imersão do substrato ouro na solução etanólica dos tióis, sugerindo que o processo de transferência de elétrons ocorre através dos pinholes da superfície e por tunelamento. Os eletrodos com as monocamadas de ácido 3-mercaptopropiônico (MPA) e o ácido tioláctico (TLA) obtiveram melhor recobrimento da superfície no tempo de imersão de 3 horas. Enquanto que o ácido 11-mercaptopropiônico (MUA) e a cistamina (CYS) necessitaram de maior tempo de imersão para organização da monocamada, de 24 horas, devido o MUA ser uma molécula de cadeia longa e a CYS devido a quebra da ligação S-S. O tamanho da cadeia do tiol influenciou no empacotamento da superfície, tióis de cadeia curtas tendem a formar monocamadas com uma quantidade de defeitos considerável, levando ao um menor recobrimento na superfície eletródica. O MUA que contém um número elevado de carbonos na cadeia apresentou um maior recobrimento da superfície, o que ocasionou perda da resposta voltamétrica. A rugosidade e a área ativa dos diferentes eletrodos, calculadas a partir dos voltamogramas, diminuíram com a formação das monocamadas sobre a superfície do ouro. Com o objetivo de estimar a quantidade de moléculas imobilizadas sobre a superfície, foram calculados os excessos superficiais por meio da carga voltamétrica obtida da dessorção redutiva. Os valores obtidos foram de = 1,88x10-10 para Au-CYS, 5,03x10-10 para Au-MPA, 1,06x10-8 para Au-MUA e 1,35x10-10 mol.cm-2 para o Au-TLA, demonstrando uma cobertura quase completa dos sítios ativos da superfície. Pela técnica de espectroscopia de impedância eletroquímica foi possível determinar os parâmetros cinéticos das SAMs, os quais foram consistentes com os obtidos pelos voltamogramas cíclicos. Analisando o desempenho dos sensores para a determinação de dopamina (DA) através da VC, verificou que a SAM formada pelo TLA foi a que apresentou resultados mais satisfatórios quanto a sensibilidade e seletividade em relação a este analito. Estudos em diferentes velocidades de varredura para os eletrodos Au-MPA, Au-TLA e Au-CYS na presença do analito mostraram que a corrente de pico anódica aumenta linearmente com a raiz quadrada da velocidade de varredura, indicando que o processo de transferência de elétrons é controlado pela difusão das espécies à superfície do eletrodo. A dopamina foi quantificada pela técnica de VC e VOQ, na faixa linear de 1,1 a 6,6x10-7 mol L-1 com limites de detecção de 1,42x10-7 mol L-1e 4,77x10-8 mol L-1, respectivamente. Utilizando-se a técnica de VOQ, o eletrodo Au-TLA foi capaz de distinguir o ácido ascórbico (AA) e DA quando presentes na mesma solução, com uma diferença de potencial de aproximadamente 340 mV.

Gold electrocatalysts have been of growing interest in recent years owing to their reactivity for a variety of important reactions such as the oxygen reduction reaction. This activity has been shown to be dependent on the size of the supported electrocatalyst nanoparticles. In this thesis the effects of Au nanoparticle size are explored for the oxygen reduction, ethanol oxidation and carbon monoxide oxidation reactions (Chapter four). The results show the oxygen reduction and ethanol oxidation reactions were favoured using larger particles, 6 nm in diameter, whilst the CO oxidation reaction was more facile on smaller particles, 3 nm in diameter. The effects of size are attributed to the size dependent strength of the Au-O (H) bond. Modified Au nanoparticles, in which the Au serves as a core for a Pt or Pd shell have also been of recent interest, as Au has been less expensive than Pt. These core-shell electrocatalysts thus affect both cost and activity advantages as the underlying Au core affect the properties of the shell. In this thesis the effects of the particle size of the Au core on the activity of Pt or Pd shells have been investigated (Chapter five). The results show that the oxygen reduction reaction is well again more facile when the core size is larger, whilst the ethanol oxidation reaction now is favoured with the small Au core size. The coverage of Pt or Pd on the Au core was also found to be dependent on the particle size, with smaller particles being covered by thinner shells. Thus, the size dependence of the oxygen reduction activity is once again attributed to O (H) coverage and bond strength, whilst the ethanol oxidation is attributed to either an electronic perturbation of the Pt or Pd by the Au core of an ensemble effect.

L'objectif de l'étude est l'application d'un procédé basé sur la lixiviation statique suivie de l'électrolyse directe (LSED) a la valorisation de petits gisements d'or, notamment les petits gisements amazoniens du brésil dont la production représente 75% de l'or produit dans ce pays, bien que compte tenu des techniques artisanales utilisées les taux de récupération de l'or ne dépassent pas 30 à 40% comme le montre l'état de l'art. Le procédé LSED a été appliqué à 3 minerais types différents quant aux métaux accompagnateurs et à la para genèse: il s'agit du minerai du chapeau de fer du gisement du rouez (France), du filon de quartz d'essakane (Burkina Faso) et du minerai sulfure complexe de volta grande (Brésil). Les taux de mise en solution varient de 70 à 90%. L'électrolyse directe effectuée sur les solutions de lixiviation diluées (3 à 8 mg au/l) permet d'atteindre des rendements d'électrodéposition très élevés, mais alors les rendements faradiques sont très bas et par conséquent les consommations énergétiques très élevées. L'analyse des dépôts électrolytiques au microscope électronique à balayage montre des structures non orientées, plurimétalliques et de morphologie variable. Le procédé LSED peut s'appliquer industriellement a un minerai d'or pauvre en métaux accompagnateurs, avec lixiviation en tas de 2000 t et en employant des électrolyseurs d'un volume unitaire de 1000 l minimum. Dans ce cas, après environ 7 h d'électrolyse directe, on peut récupérer 60% de l'or avec une consommation d'environ 800 kwh/kgau

Thesis (Ph.D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009.
Committee Chair: Janata, Jiri; Committee Member: Bunz, Uwe; Committee Member: Collard, David; Committee Member: Josowicz, Mira; Committee Member: Kohl, Paul.

Nowadays it is attached to a major effort to study applications of nanoparticles in biosensors technology. We studied the effect of gold nanoparticles on the surface of the electrodes by Electrochemical Impedance Spectroscopy method and Cyclic Voltammetry. For impedance measurements was proposed substitute electrical model and cyclic voltammetry method was used to determine the electroactive surface of electrodes.

Submitted by Erika Demachki (erikademachki@gmail.com) on 2017-03-14T18:52:47Z No. of bitstreams: 2 Dissertação - Elter Gouveia Gama - 2016.pdf: 9144026 bytes, checksum: d1fc24837019fb8951a0853874963512 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)
Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-03-20T12:24:25Z (GMT) No. of bitstreams: 2 Dissertação - Elter Gouveia Gama - 2016.pdf: 9144026 bytes, checksum: d1fc24837019fb8951a0853874963512 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)
Made available in DSpace on 2017-03-20T12:24:25Z (GMT). No. of bitstreams: 2 Dissertação - Elter Gouveia Gama - 2016.pdf: 9144026 bytes, checksum: d1fc24837019fb8951a0853874963512 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-06-21
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
The present paper concern to the electrochemical characterization of the gold electrodeposition process into a carbon paste (CP) to produce graphite powder covered by gold. This electrode also was used to study the voltammetric features of dopamine oxidation. The voltammetric study of gold electrodeposition process indicated that for MCPE-oily, the reduction of AuCl4 - occurs from potentials more negative than ~+0.60 V (peak at ~+0.35 V) and gold oxidation from potential more positive than ~+0.40 V (peak at +0.65 V). For MCPE-aqueous, without and with glycerol, the reduction of AuCl4 - occurred from potentials more negative than ~+0.73 V (peak at ~0.40 V) and the gold oxidation from more positive potentials than ~ +0.25 V (peak at +0.57 V). These processes were dependents on the gold ion concentration into the CP. It was also verified that the Au(III) reduction probably occurred throughout of the MCP volume, but not homogeneously. It was verified that the reduction process takes place preferably in the MCP interface/aqueous NaCl solution and decreased toward the interior of the PC. In addition, it was observed that the process of gold electrodeposition on the MCPE behaves as a quasi-reversible system, thereby indicating that the system has a strong dependence on the mass transport (diffusion and migration) and electron transfer. In addition, it was found that the cathodic peak currents for MCPE-aqueous were higher than the MCPE-oily, indicating that the reduction kinetics in aqueous medium is highest, probably due to the increase in the mass transport rate in aqueous solution. Studies using factorial design with the oily and aqueous MCPE indicated that the factors: HAuCl4 concentration in the PC, deposition charge and the additive presence affected the performance of the MCPEs in ferrocyanide solution. Micrographs obtained by scanning electron microscopy (SEM) for oily and aqueous MCPE indicated that the gold electrodeposit occurred on some graphite flakes with an homogeneous layer of gold. The TEM images of the graphite powder with gold electrodeposit for MCPE-oily showed gold particles with dimensions of 52.1 nm to 281.5 nm distributed evenly over the graphite flake. X-ray diffraction analisys indicated that the gold electrodeposit was polycrystalline. The dopamine (DA) oxidation was dependenting on the electrodeposition parameters and DA solution composition. The analytical curve for the DA oxidation in NaCl/NaS2O5 did not provide adequate linearity, being influenced by the DA/NaS2O5 ratio and acidity solution.
O presente trabalho trata da caracterização eletroquímica do processo de eletrodeposição de ouro dentro de uma pasta de carbono (PC) para produzir pó de grafite recoberto com ouro. Este eletrodo também foi utilizado para estudar o perfil voltamétrico da oxidação de dopamina. O estudo voltamétrico do processo de eletrodeposição indicou que para o EPCM-oleoso a redução de AuCl4 - ocorre a partir de potenciais mais catódicos que ~+0,60 V (pico em +0,35 V), e a oxidação de ouro a partir de potenciais mais anódicos que ~+0,40 V(pico em +0,65 V). Para o EPCM-aquoso sem e com glicerol a redução de AuCl4 - ocorreu a partir de potenciais mais negativos que ~+0,73 V (pico em ~0,40 V) e oxidação de ouro ocorre a partir de potenciais mais positivos que ~+0,25 V (pico em +0,57 V). Estes processos foram dependentes da concentração de íons ouro na PC. Verificouse também, que a redução do Au3+ provavelmente ocorre em todo o volume da PCM, porém não homogeneamente. Quanto a extensão da eletrodeposição, observou-se que o para os EPCMs oleosos e aquosos o processo de redução ocorre preferencialmente na interface PCM/solução aquosa de NaCl e diminuiu em direção ao interior da PC. Ademais foi observado que o processo de eletrodeposição de ouro no EPCM comporta-se como um sistema quase-reversível, indicando com isso que o sistema tem uma forte dependência do transporte de massa (migração e difusão) e transferência de elétrons. Ademais, observou-se que as correntes de pico catódico para os EPCMs aquoso foram maiores do que os EPCMs oleoso, indicando que a cinética de redução em meio aquoso é maior possivelmente devido a maior velocidade no transporte de massa no meio aquoso. Estudo por planejamento fatorial realizado com EPCM oleoso e aquoso indicou que os fatores (concentração de HAuCl4 na PC, carga de deposição e presença de aditivo) afetaram a performance dos EPCMs em solução de ferrocianeto. Micrografias obtidas por microscopia eletrônica de varredura (MEV) para o EPCM oleoso e aquoso indicaram que a eletrodeposição de ouro ocorreu sobre algumas placas de grafite com uma camada homogênea de ouro. As imagens de MET do pó de grafite com ouro eletrodepositado para o EPCM oleoso mostraram partículas de ouro com dimensões de 52,1 nm a 281,5 nm, distribuídas sobre as placas de grafite. Análise por difração de raios X, indicou que houve eletrodeposição de ouro policristalino no pó de grafite. A oxidação de dopamina foi dependente dos parâmetros de eletrodeposição e da composição da solução de DA. A curva analítica para a oxidação DA em NaCl/Na2S2O5 não apresentou linearidade adequada, sendo influenciada pela razão DA/ Na2S2O5 e acidez da solução.

Émanant d’une collaboration entre le laboratoire CNRS du GREMI et le CEA le Ripault, l’objectif de cette thèse est de réaliser une étude exhaustive sur les conditions d’élaboration des électrodes de pile à combustible PEMFC par procédés plasma, dont l’enjeu est d’améliorer l’activité électro-catalytique du catalyseur employé qu’est le platine (Pt). A même quantité, la répartition du platine sur son support se révèle être un critère déterminant sur les performances délivrées par les PEMFCs. De cette observation, plusieurs axes de recherche ont été proposés et chacun d’entre eux a permis d’obtenir de nouveaux résultats. Le régime de pulvérisation magnétron à haute puissance pulsée (HiPIMS) est étudié dans le cas de dépôt de matériaux nobles pures (Pt, Au, Pd) et alliés (Pt5Pd95 et Pt50Pd50) et a permis de révéler une vapeur métallique ionisée conséquente lors du dépôt (10 % à 90 % selon l’élément). Les résultats obtenus sur le régime HiPIMS ont permis la modification de la distribution d’une faible quantité fixée de Pt (20 μg.cm−2) déposée sur la profondeur des couches de diffusion des gaz (GDL), améliorant incidemment les performances des PEMFCs (+80 % à 0.65 V, la tension à puissance nominale). Ce résultat est complété par ceux obtenus sur l’élaboration de catalyseur alliés, notamment sur la disposition du matériel catalytique au niveau de la structure des agrégats (+93 % à 0.65 V pour Pt5Pd95 en dépôts successifs). Une autre étude a permis d’étudier la modification de répartition du Pt en contact avec la membrane électrolyte. La surface de membrane échangeuses de proton est alors initialement structurée. Ces structurations de surface des membranes montrent une amélioration globale des performances PEMFCs pour les architectures CCB (Catalyst Coated Backing) et CCM (Catalyst Coated Membrane) d’un facteur 1.3 jusqu’à 12, respectivement
From a collaboration between the CNRS laboratory of the CEA and GREMI Ripault, the objective of this thesis is to conduct a complete study on the conditions for producing electrodes of PEM fuel cell by plasma processes in order to improve the electro-catalytic activity of the catalyst (Pt). The platinum atoms on its support appears to be a one of the most important factor determining the performance delivered by the PEMFCs. From this observation, several lines of research have been proposed and each of them has yielded new results. The High Power Impulse Magnetron Sputtering (HiPIMS) process is studied in case of depositions of noble materials (Pt, Au, Pd) and alloy (Pt5Pd95 and Pt50Pd50) and revealed an ionized metal vapor consequent upon deposition (10 % to 90 % depending of the element). The results obtained on the HIPIMS process have allowed a change in the distribution of a small fixed amount of Pt (20 μg.cm−2) deposited on the depth of the gas diffusion layer (GDL), incidentally improving the performance of PEMFCs (+80% at 0.65 V, the voltage at rated power). This result is complemented by those obtained on the development of allied catalysts, especially with the arrangement of the catalytic material on the aggregates structure (+93 % at 0.65 V for Pt5Pd95 in successive deposits). In order to modify the Pt atoms distribution on the membrane support, another study has been realized. The surface of the proton exchange membrane has been structurated before the Pt deposition. Such structuration have shown an increase of the overall performance of PEMFCs in the case of CCB (Catalyst Coated Backing) and CCM (Catalyst Coated Membrane) architecture with an improvement factor of 1.3 up to 12, respectively

A potencialidade do eletrodo de cobre em meio alcalino foi demonstrada para o determinação de etanol a +0,6 V vs Ag/AgCl. A participação de espécies solúveis de Cu(III) no processo eletrocatalítico envolvendo a oxidação do etanol foi demonstrada por experimentos utilizando eletrodo disco-anel. A influência do potencial de pré-tratamento no sinal anódico foi investigada e correlacionada com a morfologia dos filmes formados na superfície do eletrodo por EDS (Energy Dispersive X-Ray Spectroscopy), indicando que as espécies de Cu(III) são originadas a partir da oxidação da camada de CuO. As medidas de etanol foram realizadas por amperometria em 0,6 V (vs Ag/AgCl). A repetibilidade das medidas utilizando padrão aquoso de etanol 0,05 % (v/v) foi de 3 % (v/v) e os limites de detecção e quantificação foram de 0,005 % (v/v) e 0,01 % (v/v), respectivamente. Nas condições experimentais otimizadas, o sensor amperométrico foi utilizado para o monitoramento da concentração de etanol no ar exalado (BrAC), que foi convenientemente coletado em um balão de borracha (V = 3 L) e introduzido em uma solução de NaOH 1 mol L-1 (V = 10 mL). O sensor apresentou uma faixa linear para concentrações de etanol em ar exalado na faixa de 0,26 – 130 mg L-1, operando de acordo com os parâmetros analíticos especificados na Legislação Brasileira para a quantificação de etanol no ar exalado em condutores de veículos automotores. A constante de eliminação de etanol do corpo humano também foi investigada e os resultados concordaram com os valores da literatura. Empregando-se eletrodos de Cu e Au foram também desenvolvidas outras metodologias para a quantificação de dipirona, glicose e ácido ascórbico e sistemas em fluxo. Estudos sobre o desenvolvimento e propriedades de um sistema gerador-coletor foram realizados e o dispositivo foi utilizado em titulações de substâncias redutoras com iodo gerado eletroquimicamente.
A copper disc working electrode in alkaline solutions was demonstrated to act as a suitable amperometric sensor for ethanol determination at +0.6 V vs Ag/AgCl. The participation of free-soluble Cu(III) species in the electrocatalytic process involving the anodic oxidation of ethanol has been demonstrated by rotating ring-disc electrode voltammetry. The influence of the pretreatment potential on the anodic signal was investigated and a correlation with the morphology of the electrode surface characterized by Energy Dispersive X-Ray Spectroscopy (EDS) indicated that the Cu(III) species is originated from the oxidation of a CuO layer. Ethanol measurements were performed in the amperometric mode at 0.6 V (vs Ag/AgCl). The repeatability of the measurements for a 0.05 % aqueous ethanol solution was estimated as 3 %, and the detection and quantification limits were determined as 0.005 % and 0.01 %, respectively. At the optimum experimental conditions, the amperometric sensor was used to monitor the concentration of ethanol in breath (BrAC), which was conveniently collected in a rubber air balloon (volume = 3 L) and introduced in a 1 mol L-1 NaOH working solution (volume = 10 mL). The sensor can measure a person\'s breath ethanol over the concentration range 0.26 - 130 mg L-1 by operating it according to an established protocol, of which the analytical parameters are specified by the Brazilian Legislation for BrAC measurements in drivers. The rate of ethanol degradation in the body was followed, and the results agree with predictions in the literature. Methodologies for the determination of dipyrone, glucose and ascorbic acid were also developed by using Cu and Au electrodes. Features of a dual-band electrochemical cell were investigated towards the development of a generator-collector system, which was employed in titrations with electrogenerated iodine.

Interfacial investigations of a protein monolayer electrochemical system, cytochrome c (cyt c) adsorbed to a carboxylic acid (COOH) terminated self-assembled monolayer (SAM) were undertaken. Previous research suggested that anomalous peak broadening observed in the voltammetry of cyt c may be the manifestation of surface effects at the SAM/solution interface (heterogeneous adsorption sites). To examine this matter further, research was directed at 1) deciphering the role of the gold substrate's topography in both SAM formation and cyt c voltammetry; 2) understanding the protein binding interactions at the SAM/solution interface that influence cyt c adsorption and electrochemical response, and 3) investigating the microscopic properties of all the surfaces involved. Electrochemical and scanning probe microscopy techniques were used to explore the influence of gold topography in cyt c / COOH SAM / Au systems. COOH SAMs (11-mercaptoundecanoic acid and 14-mercaptotetradecanoic acid) were prepared and characterized on a variety of gold surfaces including evaporated, bulk, single crystal, and expitaxially grown on mica gold substrates. Each type of gold surface exhibited specific topographical features and characteristic roughness. SAMs were found to have a decreasing number of defects as the topography of the gold became smoother, as evidenced by an increased ability to block solution probe molecules. As the SAMs become less defective on the smoother gold, the extent of adsorption and the magnitude of the electrochemical response of adsorbed cyt c decreased significantly. These results show cyt c adsorption and electrochemistry to be intimately related to the density of defects in the SAM, which, in turn, are heavily influenced by the gold topography. Additionally, as the gold roughness decreased, the double layer capacitance of the films was observed to increase. A physical model was proposed in which the structure and properties of COOH SAMs are dictated by significant endgroup interactions in addition to chain-chain interactions. The model illustrates how gold topography plays an intricate role in determining the structure and application of COOH terminated SAMs. Research was also performed on the SAM/solution interface by thermally healing SAMs on gold and utilizing SAMs on Ag-UPD modified gold. Thermal healing, by reducing the number of defects in the SAMs, was also found to affect both SAM structural properties and cyt c adsorption. SAMs that had been thermally healed exhibited a lower density of defects while, at the same time, supported lower electroactive cyt c coverage. Ag UPD layers were tested as a means of creating more stable, less defective COOH SAMs for cyt c immobilization and possibly allowing for more ideal voltammetry of the proteins. Preliminary research has shown that SAMs with Ag-UPD layers have fewer defects and greater inherent stability. Finally, scanning probe microscopy techniques were employed to investigate the structure of the gold substrate, the SAM/solution interface, and adsorbed cyt c. In addition to cyt c / SAM / Au research, results from the following investigations are presented: electrochemistry of adsorbed cyt c at indium tin oxide electrodes and the electron transfer (ET) properties of iron-sulfur metallodendrimers. The metallodendrimers exhibited attenuated ET properties with increasing generations of dendritic ligands in a solventless, polymeric media. The electrochemistry of Cu(II) in physiological pathways that may be related to neurological and ocular diseases was also explored. Research on these systems revealed that the reduction of Cu(II) by certain peptides and catabolites may play a vital role in the development of these diseases.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior
O presente trabalho ilustra o desenvolvimento de uma rota sintÃtica para a obtenÃÃo de uma meso-metaloporfirina, a partir de uma meso-porfirina base livre, macromolÃcula derivada do LÃquido da Casca da Castanha de Caju (LCC), subproduto do agronegÃcio do caju. A obtenÃÃo dessas espÃcies seguida de estudos preliminares da modificaÃÃo da superfÃcie do eletrodo de ouro com a meso-metaloporfirina de cobre com aplicaÃÃo para sensor de NO (Ãxido NÃtrico) tambÃm compÃe os objetivos desse trabalho. A partir do processo de metalaÃÃo,foi sintetizada uma meso-metaloporfirina utilizando Cu (II) como centro metÃlico, a partir da macromolÃcula base livre, e testes voltamÃtricos foram realizados utilizando o eletrodo de ouro, em meio de diclorometano e PTBA 0,1 mol L-1, obtido a 100 mV s-1.Estudos foram realizados a cerca do comportamento eletroquÃmico dos filmes formados em presenÃa de NO em meio aquoso de Na2SO4 0,5 mol L-1 obtendo o voltamograma cÃclico para o eletrodo de ouro modificado com a porfirina de cobre(II) na detecÃÃo de NO e foi observado no voltamograma para NO sobre uma intensidade de corrente 7,6 vezes maior comparada à do pico observado para o mesmo processo do NO na superfÃcie de ouro nÃo modificado demonstrando elevado potencial para aplicaÃÃo como sensor eletroquÃmico. Outra metodologia eletroanalÃtica foi desenvolvida para a obtenÃÃo de um biossensor, baseado em uma enzima, glutationa-S-transferase (GST), para determinaÃÃo do pesticida molinato, um herbicida prÃ-emergente, em amostras reais de Ãgua de campos de arrozais da cidade do Porto, em Portugal. A construÃÃo deste biossensor baseou-se a imobilizaÃÃo de GST em um eletrodo de carbono vÃtreo (GCE), atravÃs da ligaÃÃo covalente glutaraldeÃdo-amino-silano (APTES/GA). O princÃpio deste biossensor consistiu no processo de inibiÃÃo da GST promovida pelo molinato. A curva de calibraÃÃo foi obtida por meio da tÃcnica de voltametria de pulso diferencial (VPD) variando a concentraÃÃo do pesticida entre 1,01x10-6 â 4,20x10-5 mol L-1 apresentando um limite de detecÃÃo (LD) de 0,064 mg L-1. O biossensor baseado na GST foi aplicado para quantificar o molinato nas amostras de Ãgua das lavouras de arrozais. Os resultados obtidos com este biossensor foram comparados com aqueles obtidos por HPLC e nÃo houve diferenÃas estatisticamente significativas comprovando, entÃo, que a metodologia desenvolvida foi precisa no nÃvel de concentraÃÃo estudada.
This study illustrates the development of synthetic route will be obtaining meso-metalloporphyrin, from porphyrin meso-free base macromolecule derived from Shell Liquid Cashew Nut (CNSL), byproduct of cashew agribusiness. Obtaining these species followed by preliminary studies of surface modification of gold electrode with copper meso-metalloporphyrin with application to sensor of NO (Nitric Oxide) also composed the objectives of this work. From metalation process, was synthesized by meso-metalloporphyrin using Cu (II) the a metal to center, from the macromolecule free base, and voltametric tests were carried out using the gold electrode in the middle of dichloromethane and TBAP 0,1 mol L-1, obtained at 100 mV s-1. Studies have been conducted about the electrochemical behavior of the films formed in the presence of NO in aqueous Na2SO4 0,5 mol L-1 the cyclic voltammogram obtained will be the gold electrode modified with porphyrin to copper (II) the detection of NO and voltammogram was observed in about one NO to current intensity 7,6 times larger compared to the peak observed for the same process of NO in unmodified gold surface showing high potential for application as an electrochemical sensor. Electroanalytical another methodology was developed will be obtaining the biosensor, based on an enzyme, glutathione-S-transferase (GST), will be determining the pesticide molinate, the real daily pre-emergent herbicide in samples of to water of paddy fields City Porto, in Portugal. The construction of this biosensor was based on the immobilization of GST in glassy carbon electrode (GCE) by covalent glutaraldehyde-amino-silane (APTES/GA). The principle of this biosensor consisted of the process promoted by inhibition of GST molinate. The calibration curve was obtained by the technique of differential pulse voltammetry (DPV) varying the concentration of the pesticide between 1,01 x10-6 to 4,20 x10-5 mol L-1 having a limit of detection (DL) of 0,064 mg L-1. The biosensor based on GST was applied to quantify the molinate in water samples of paddy crop. The results obtained with this biosensor were compared with those obtained by HPLC and no statistically significant differences proving therefore that the developed methodology has been studied in terms of concentration.

碩士
國立交通大學
材料科學與工程學系奈米科技碩博士班
108
When developed country has become more industrialization and its citizens’ life expectancy is increasing, civil diseases like diabetes also have emerged and the related biomedical materials have gradually gained the attention of the world. The biomedical materials studied in this research can be divided into two parts. The first part is Comparison and study of increasing the surface area of gold electrode by etching and electrochemical methods.The other is the study of Nanoporous gold surface modified by anti-fouling material for Blood glucose sensing application. The first part is to use etching and electrochemical methods to increase the surface area of the materical. The etching uses iodine to make its Roughness increase via chemical action.When using electrochemical methods, the most important thing is to use chloride ions at a certain voltage. It will carry out the process of electrolysis, electrodissolution, disproportion and deposition of Au In this research, we focus on the interaction between KCl concentration and pH value, the standardized area of gold electrode and the optimized potential of anodizing in order to find the best condition for preparing nanoporous gold and analyze its surface structure. The second part study uses nanoporous gold as electrode made in the previous study in order to test which oxidation current for glucose is largr and find applied voltage at maximized current signal in a mixed of glucose with interferent solution. Then we synthesizes PFB-CK and PFB-CK salt; the latter has zwitterion properties. And then; we combine PFB-CK and PFB-CK salt with nanoporous gold made in the first part in sulfur-gold bond by using self-assembly respectively. Next, we measure the related current signal experiments of the electrode in the glucose solution, such as detection limit and linear range and then undergo the anti-cell fouling test, bradford protein assay and MTT assay. It has been confirmed by experiments that the modified electrode has anti-cell and protein fouling and high biocompatibility, and its long-term stability is better than the electrode made of bare nanoporous gold.

碩士
國立成功大學
化學系專班
94
There are three parts in this study : the first part is using nanoporous-Au electrodes and Osteryoung square wave voltammetry to determinate L-cysteine and glutathione in aqueous solution, individually. In the case of L-cysteine, if preconcentration time is 10 mins,the linear dynamic range is 15-160 μM, and the detection limit is 0.1 μM(3s). For the determination of glutathione, with a preconcentration time is 5 mins, and the linear dynamic range is 0.5-25 μM, and the detection limit of < 0.5μM. The second part of this study, use the GSH/nenoporous-Au electrode to determinate the copper ion in aqueous solution. If preconcentration time is 5 mins, the linear dynamic range is 0.79-315 nM, and the detection limit is < 0.79 nM. In the third part, a nanoporous-Au electrode and electrochemical catalytic reaction were employed for the determination of Se(IV) in aqueous solution. Good sensitivity was achieved through the catalytic process between selenium and bromate. Follow potentiostat, linear calibration graph was obtained over the range 20-2000 ppb of Se(IV), with a detection limit (3 x blank signal) of 2.4 ppb.

碩士
國立交通大學
應用化學系所
95
In this study, novel nanostructures of metal gold were discovered, including sheet, flower, wire and coralloid shapes. We demonstrated the synthesis of gold nanostructures via Galvanic displacement reaction. We found that cetyltrimethylammonium chloride (CTAC) played an important role to affect the morphology of the products. Au nanosheets, nanoflowers and nanowires were derived by using Cu metal as the reductant in the presence of CTAC on carbon electrodes. The diameters of single crystal Au nanowires, reducted from HAuCl4 by Cu metal, were 15-25 nm, and the lengths were 300-500 nm. Each nanowire exhibited single crystallinity with the growth in [110] orientation. In addition, Au nanowires, diameters 50-100 nm and lengths up to several tens μm, were prepared by reacting HAuCl4(aq) with Sn metal and CTAC on a carbon electrode. Furthermore, surface-enhance Ramen scattering (SERS) spectra of P-NTP (p-nitrothiophenol) on the as-prepared carbon electrode with gold nanowires was measured. We also used electrochemical synthesis method to produce gold nanocoralloid.

碩士
長庚大學
化工與材料工程學系
98
The anodic behaviors of gold electrode as anode catalyst using in direct borohydride fuel cells were investigated to collect the parameters for single cell measurements. To avoid the hydrolysis reaction of sodium borohydride in producing hydrogen and to promote the direct electrochemistry reaction of borohydride to 8 electrons transfer are the key issues of DBFC. The by-product (hydrogen) of sodium borohydride can be measured in the half-cell measurements and single cell measurements were controlled by using the parameters taken in half-cell measurements. Carbon supported gold electrocatalysts were used in DBFC single cell measurements and the half-cell measurements indicate the gold electrode area promote anode electrochemical reactions. The rotating disk electrodes measurements may provide the flow rates parameters for DBFC single cell operations and the anode flow rate of 80ml/min was taken.

碩士
國立中央大學
化學工程與材料工程學系
104
With the rapid development of technology, biosensors have been used extensively in medical detecting. Glucose biosensors, which have become the convenient and mature product, have great economic value because of huge consume in the world. In this study, in order to prepare lower cost gold electrode glucose biosensors, the screen printed substrate which contained palladium catalyst was prepared. The effects of contents of palladium on the performance of biosensor was investigated. A reactor for electroless plating was designed. Nickel, palladium and gold were deposited on the substrate in order to increase the conductivity of electron passed through the sample. The operating parameters such as temperature, time, hardness and thickness were changed to study their effects on the stability of product. The samples were then doped by the enzyme to check the performance of glucose biosensors. The samples were characterized by focused ion beam (FIB), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results illustrated that the better operating conditions of electroless reactors for nickel, palladium and gold was at the region of temperature and dipping time.

碩士
國立交通大學
應用化學系所
97
It has been paid much attention to develop nonenzymatic glucose electrochemical sensor by inorganic metal、metal oxid or alloy nanometerial, which would eliminate the instability problem of enzymatic glucose sensor. In this study, A disposable gold nanoparticles (AuNPs) modified ITO electrode, which the effect area was fixed by photolithography and etching technique, has been developed only with single step electrodeposition for glucose sensing. The AuNPs film on the electrode was formed by dipping the ITO electrode into the mixed solution containing 400 mg/L HAuCl4 and 0.01% chitosan and giving a reduction potential at -0.8 V (vs. Ag/AgCl) for 60 minute. The layer of the stacked AuNPs on the ITO surface was very stable and the nanostructure of this AuNPs modified sensor was performed by field-emission scanning electron microscope (SEM). After eliminating common interferences by Nafion�� covering, the analytical performance of the electrode for glucose detection was investigated. The sensitivity and the detection limit of the electrode were 107.7 µA/mMcm2 and 1.46 µM respectively in amperometric glucose sensing in 0.1 M NaOH solution. Linear range was from 5 µM to 2.3 mM (R2 = 0.9991). Since the ITO glass was obtained by low cost industrial production with stable quality, this substrate can be used as disposable material of sensor fabrication.

碩士
中原大學
奈米科技碩士學位學程
98
Gold nanowires were successfully fabricated by electrochemical deposition using polycarbonate membranes (PC) as the growing templates. The Au nanowire electrodes were modified by three methods which enhanced the response of sensibility in different ways. The nanowire electrode was employed to be the support matrix for the immobilization of hemoglobin (Hb).. Therefore, the Hb-modified Au nanowire electrode could be used as a biosensor with high sensitivity for Hb. The 3D electrode has a larger surface area than that of flat electrode and the sensitivity of electrode for hemoglobin (Hb) was enhanced. The electrode of gold nanowires modified by glucose oxidase (GOD) is suitable for application as a glucose sensor. The cyclic voltammorgrams (CV) demonstrated that the response current of glucose was enhanced by using GOD-modified Au nanowires working electrode. Enhanced cyclic voltammorgrams were also obtained using Fe3O4 nanoparticals modified gold nanowires as the working electrode. It is thought that the electron transfer between Fe2 + and Fe3 + ions helped the activity of ferricyanide.

碩士
國立臺灣大學
化學工程學研究所
91
In the thesis, alkyl thiols are used to form oriented self-assembly monolayers. Oriented monolayers offer the possibility of precise control of spacing and orientation on a molecular level. It was reported that self-assembly monolayers formed from alkyl thiols are remarkably stable in aqueous solution. This research is mainly carried out by electrochemical analysis techniques, trying to find out the effect of electron transfer by tunneling across the monolayers. The rotating disk system was applied to study the electrochemical reaction mechanisms. Furthermore, the distribution morphology of alkyl thiols on gold was observed by atomic force microscopy (AFM). The cleansing condition of gold surface affects electrochemical reactions seriously. It is essential to clean electrodes completely before electrochemical experimental analysis. Three different alkyl thiols R-SH（R=CnH2n+1，n=4、8、12）were used in this study. And because alkyl thiol can’t take redox reactions, redox species are added into the electrolyte. Then the effect of different chain length to redox reactions can be discussed. One of the redox species in the study is ferricyanide-ferrocyanide couple that is often used in the previous studies; another redox specie cobalt bipyridine Co(bpy)33+is synthesized in this study. As the alkyl chain length of thiols on gold electrode increases, the conductivity of gold electrode will decrease, the redox reaxtion will derivate from reversible reaction more and more obviously. The inhibition of thiol modified gold electrode to the diffusivities of Fe(CN)63-/4- and Co(bpy)33+/2+ couples are also discussed in the thesis. For 1-octanethiol modified gold electrode, the diffusivity of Fe(CN)63- decreases from 7.25×10-6 cm2/s to 5.70×10-6 cm2/s, and the diffusivity of Co(bpy)33+ decreases from 1.52×10-6 cm2/s to 7.56×10-7 cm2/s. As the alkyl chain length of thiols on gold electrode increases, the reaction rate constants decrease at the same time. Especially for the dodecanethiol modified gold electrode, the thickness of self-assembly monolayer is larger, and molecule will arrange much closer. As a result, the redox couples are almost kept out of the gold surface. For dodecanethiol modified gold electrode, the rate constant of 1mM Fe(CN)63- decreases from1.39×10-1 s-1 to 7.40×10-4 s-1, and the rate constant of 1mM Co(bpy)33+ decreases from 2.49×10-2 s-1 to 2.15×10-3 s-1.It was found that the current and the reaction rate of thiol modified gold electrode in Co(bpy)33+ solution are both decrease linearly with alkyl chain length. Therefore, it is more correct to determine the alkyl chain length from voltammograms. However, it is much more convenient to observe the current and reaction rate differences between thiol modified gold electrode and gold electrode in Fe(CN)63-/4- solution.