Relevant bibliographies by topics / Heme electrochemistry

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  1. Journal articles
  2. Dissertations / Theses
  3. Book chapters
  4. Conference papers

Academic literature on the topic 'Heme electrochemistry'

Author: Grafiati
Published: 6 September 2023

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Journal articles on the topic "Heme electrochemistry"

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Samajdar, Rudra N., Dhivya Manogaran, S. Yashonath, and Aninda J. Bhattacharyya. "Using porphyrin–amino acid pairs to model the electrochemistry of heme proteins: experimental and theoretical investigations." Physical Chemistry Chemical Physics 20, no. 15 (2018): 10018–29. http://dx.doi.org/10.1039/c8cp00605a.

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Udit, Andrew K., and Harry B. Gray. "Electrochemistry of heme–thiolate proteins." Biochemical and Biophysical Research Communications 338, no. 1 (December 2005): 470–76. http://dx.doi.org/10.1016/j.bbrc.2005.08.087.

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Todorovic, Smilja, Catarina Barbosa, Lidia Zuccarello, and Celia M. Silveira. "Vibrational Spectro-Electrochemistry of Heme Proteins." ECS Meeting Abstracts MA2022-01, no. 14 (July 7, 2022): 963. http://dx.doi.org/10.1149/ma2022-0114963mtgabs.

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Heme proteins perform a plethora of distinct cellular functions, including e.g. electron transport (ET), energy conversion, detoxification, catalysis, signaling, and gene regulation, and as such inspire a myriad of biotechnological applications. We use resonance Raman (RR) and Surface enhanced RR (SERR) spectroscopies to probe the architecture of the heme pocket in diverse heme proteins and enzymes, which is essential for the understanding of their physiological properties as well as for the evaluation of their potential for development of the 3rd generation bioelectronic devices (1,2). Moreover, plasmonic metal that gives origin to the surface enhancement of the Raman signal of the molecules found in its close proximity can serve as an electrode, thus driving electrochemical processes. In the case of heme proteins attached to plasmonic Ag electrodes, SERR spectra selectively show vibrational bands originating from the heme moiety only, which are sensitive to spin, coordination and redox state and of the heme iron. These properties that govern the catalytic performance of heme enzymes can be monitored in potential dependent manner by SERR spectro-electrochemistry. We have demonstrated that SERR spectro-electrochemistry possesses unique capacity of to i) disentangle ET processes in multi hemic proteins, such as 28 heme containing nitrite reductase, which represent a challenge for all other experimental approaches and ii) detect subtle immobilization induced structural changes in enzymes of biotechnological interest, which e.g. in the case of cytochrome P450 may prevent their successful applications (1-4). Here we show that SERRS monitoring of electrocatalytic processes by immobilized heme peroxidases, can provide information on catalytically relevant species in situ. Several members of a recently discovered family of heme dye-decolorizing peroxidases (DyPs) that possess remarkable catalytic properties in solution and high biotechnological potential, have been immobilized on biocompatible Ag electrodes. Their structural and electrocatalytic properties studied by RR, SERR spectro-electrochemistry and electrochemistry (2). The immobilized DyP from Pseudomonas putida (PpDyP), in particular, shows native structure and outstanding analytical and catalytic parameters, and hence an exceptional potential for development of 3rd generation biosensors for H2O2 detection. In terms of sensitivity, the bioelectrodes carrying immobilized PpDyP outperform HRP based counterparts reported in the literature (2,4). The biosensor based on a PpDyP variant that harbors mutations at the second shell of the heme cavity reveals further improved storage. Our work highlights the importance of integrated, multidisciplinary approach to simultaneously evaluate the structure and catalytic properties of the enzymes, which ensures faster identification and optimization of the promising candidates for biotechnological applications. References: 1. Silveira, C. M.; Moe, E.; Fraaije, M.; Martins, L. O.; Todorovic, S. (2020). Resonance Raman view of the active site architecture in bacterial DyP-type peroxidases. RSC Advances 10, 11095. https://doi.org/10.1039/D0RA00950D 2 Barbosa, C.; Silveira, C. M.; Silva, D.; Brissos, V.; Hildebrandt, P.; Martins, L. O.; Todorovic, S. (2020). Immobilized dye-decolorizing peroxidase (DyP) and directed evolution variants for hydrogen peroxide biosensing. Biosensors and Bioelectronics 153. https://doi.org/10.1016/j.bios.2020.112055 3 Zuccarello, L.; Barbosa, C.; Galdino, E.; Lončar, N.; Silveira, C.M.; Fraaije, M.W.; Todorovic, S. (2021) SERR Spectroelectrochemistry as a Guide for Rational Design of DyP-Based Bioelectronics Devices. Int. J. Mol. Sci. 22, 7998. https://doi.org/10.3390/ijms22157998 4 Zuccarello, L.; Barbosa, C.; Todorovic, S., Silveira, C.M. (2021) Electrocatalysis by Heme Enzymes-Applications in Biosensing. Catalysts 11, 218. https://doi.org/10.3390/catal11020218
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Grosserueschkamp, Marc, Christoph Nowak, Wolfgang Knoll, and Renate L. C. Naumann. "Time-resolved surface-enhanced resonance Raman spectro-electrochemistry of heme proteins." Spectroscopy 24, no. 1-2 (2010): 125–29. http://dx.doi.org/10.1155/2010/815817.

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Heme proteins such as cytochrome c (cc) play a fundamental role in many biological processes. Surface-enhanced resonance Raman spectroscopy (SERRS) combined with electrochemical methods is an ideal tool to study the redox processes of heme proteins. In this context we designed a new measuring cell allowing for simultaneous electrochemical manipulation and high sensitive SERRS measurements of heme proteins. The measuring cell is based on an inverted rotating disc electrode for excitation by using a confocal Raman microscope. Furthermore, we developed a SER(R)S-active silver modified silver substrate for spectro-electrochemical applications. For this purpose silver nanoparticles (AgNPs) were adsorbed on top of a planar silver surface. The substrate was optimized for an excitation wavelength of 413 nm corresponding to the resonance frequency of heme structures. An enhancement factor of 105was achieved. The high performance of the new measuring cell in combination with the new silver substrate was demonstrated using cc as a reference system.
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Mie, Yasuhiro, Kumiko Sonoda, Midori Kishita, Emil Krestyn, Saburo Neya, Noriaki Funasaki, and Isao Taniguchi. "Effect of rapid heme rotation on electrochemistry of myoglobin." Electrochimica Acta 45, no. 18 (June 2000): 2903–9. http://dx.doi.org/10.1016/s0013-4686(00)00366-2.

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Zhou, Yinglin, Naifei Hu, Yonghuai Zeng, and James F. Rusling. "Heme Protein−Clay Films: Direct Electrochemistry and Electrochemical Catalysis." Langmuir 18, no. 1 (January 2002): 211–19. http://dx.doi.org/10.1021/la010834a.

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Huang, He, Naifei Hu, Yonghuai Zeng, and Gu Zhou. "Electrochemistry and electrocatalysis with heme proteins in chitosan biopolymer films." Analytical Biochemistry 308, no. 1 (September 2002): 141–51. http://dx.doi.org/10.1016/s0003-2697(02)00242-7.

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Shen, Li, and Naifei Hu. "Heme protein films with polyamidoamine dendrimer: direct electrochemistry and electrocatalysis." Biochimica et Biophysica Acta (BBA) - Bioenergetics 1608, no. 1 (January 2004): 23–33. http://dx.doi.org/10.1016/j.bbabio.2003.10.007.

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Negahdary, Masoud, Saeed Rezaei-Zarchi, Neda Rousta, and Soheila Samei Pour. "Direct Electron Transfer of Cytochrome c on ZnO Nanoparticles Modified Carbon Paste Electrode." ISRN Biophysics 2012 (March 25, 2012): 1–6. http://dx.doi.org/10.5402/2012/937265.

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The direct electrochemistry of cytochrome c (cyt c) immobilized on a modified carbon paste electrode (CPE) was described. The electrode was modified with ZnO nanoparticles. Direct electrochemistry of cytochrome c in this paste electrode was easily achieved, and a pair of well-defined quasireversible redox peaks of a heme Fe (III)/Fe(II) couple appeared with a formal potential (E0) of −0.303 V (versus SCE) in pH 7.0 phosphate buffer solution (PBS). The fabricated modified bioelectrode showed good electrocatalytic ability for reduction of H2O2. The preparation process of the proposed biosensor was convenient, and the resulting biosensor showed high sensitivity, low detection limit, and good stability.
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Ma, X., Z. Sun, X. Zheng, and G. Li. "Electrochemistry and electrocatalytic properties of heme proteins incorporated in lipopolysaccharide films." Journal of Analytical Chemistry 61, no. 7 (July 2006): 669–72. http://dx.doi.org/10.1134/s1061934806070112.

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Dissertations / Theses on the topic "Heme electrochemistry"

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Moran, John Joseph. "Hemeproteins Bathed in Ionic Liquids: Examining the Role of Water and Protons in Redox Behavior and Catalytic Function." Cleveland, Ohio : Cleveland State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=csu1249089802.

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Thesis (Ph.D.)--Cleveland State University, 2009.
Abstract. Title from PDF t.p. (viewed on Sept.8, 2009). Includes bibliographical references (p. 101-104). Available online via the OhioLINK ETD Center and also available in print.
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Großerüschkamp, Marc [Verfasser]. "Time-resolved surface enhanced resonance Raman spectro-electrochemistry of heme proteins / Marc Groerüschkamp." 2010. http://d-nb.info/101000185X/34.

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Book chapters on the topic "Heme electrochemistry"

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Taniguchi, Isao. "Use of Promoter Modified Electrodes for Heme Protein Electrochemistry." In Charge and Field Effects in Biosystems—2, 91–100. Boston, MA: Springer US, 1989. http://dx.doi.org/10.1007/978-1-4613-0557-6_9.

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Dong, S., and T. Chen. "Electrochemistry of heme proteins on organic molecule modified electrodes." In Experientia Supplementum, 209–28. Basel: Birkhäuser Basel, 1997. http://dx.doi.org/10.1007/978-3-0348-9043-4_14.

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Marquez, Olga, and Jairo Márquez P. "Synthesis of Electrocatalysts for Electrochemistry in Energy." In Advanced Solid Catalysts for Renewable Energy Production, 300–385. IGI Global, 2018. http://dx.doi.org/10.4018/978-1-5225-3903-2.ch011.

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The increasing population demands clean and green energy, encouraging scientists and technologists to make their best effort to develop renewable, available, and low-cost acquisition of non-conventional energy. Researchers in Catalysis and Electrochemistry, working together, have reached good achievements when focused in electrochemistry studies that are under development for alternative, renewable, capture, conversion, storage, supply, uses, and applications of energy. This is called Electrochemistry in energy. The symbiosis Electrochemistry-Catalysis is fundamental in this field for successful results. Important achievements are nowadays found in literature and some of them are reported here with emphasis in the use of electrochemistry for electrosynthesis of the named photoelectrocatalysts. Thus, photoelectrocatalysts, photocatalysts, and catalysts are of importance in many of the aspects involved in the term Electrochemistry in energy. This is such a wide field, with many aspects presented here, that the authors give an appropriate view and pedagogical standpoint for the readers.
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Rad, Mohammad Behnam. "CRISPR/Cas-based electrochemical diagnostics." In Electrochemistry, 372–410. The Royal Society of Chemistry, 2023. http://dx.doi.org/10.1039/bk9781839169366-00372.

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Due to the limited time pass (less than 5 years) for developing CRISPR/Cas-based electrochemical detection platforms, this field is very new. The number of experimental studies is limited, and this field does not take a long developmental path yet. Therefore expansion of ideas is limited based on some pioneering research. However, this does not diminish the importance and potential of this field. There is vast potential in the field of CRISPR/Cas-based diagnostics; as the electrochemical detection systems proved their abilities in the past, merging these two categories will mark a bright future with applications in very diverse subjects. This chapter attempts to brighten the potential of applications in this field. Despite the limited number of researches in this field, the diverse application of CRISPR/Cas-based electrochemical biosensors are reviewed here, which implicitly confirms the potential of this field. Due to the analytical advantage of the electrochemical-based detection system, in comparison to the other methods, electrochemical CRISPR/Cas-based detection systems will significantly impact improving public health quality through developing sensitive, reliable, and affordable point of care diagnostic devices and tests.
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Schmickler, Wolfgang. "Complex reactions." In Interfacial Electrochemistry. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195089325.003.0016.

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In the past two chapters we have already encountered examples of reactions involving several steps, and introduced the notion of rate determining step. Here we will elaborate on the subject of complex reactions, introduce another concept; the electrochemical reaction order, and consider a few other examples. The simplest type of complex electrochemical reactions consists of two steps, at least one of which must be a charge-transfer reaction. We now consider two consecutive electron-transfer reactions of the type: . . . Red ⇌ Int + e- ⇌ Ox + 2e- . . .(11.1) such as: Tl+ ⇌Tl2+ + e- ⇌ Tl3+ + 2e- . . . (11.2) For simplicity we assume that the intermediate stays at the electrode surface, and does not diffuse to the bulk of the solution.
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Schmickler, Wolfgang. "Transient techniques." In Interfacial Electrochemistry. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195089325.003.0019.

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The classical electrochemical methods are based on the simultaneous measurement of current and electrode potential. In simple cases the measured current is proportional to the rate of an electrochemical reaction. However, generally the concentrations of the reacting species at the interface are different from those in the bulk, since they are depleted or accumulated during the course of the reaction. So one must determine the interfacial concentrations. There are two principal ways of doing this. In the first class of methods one of the two variables, either the potential or the current, is kept constant or varied in a simple manner, the other variable is measured, and the surface concentrations are calculated by solving the transport equations under the conditions applied. In the simplest variant the overpotential or the current is stepped from zero to a constant value; the transient of the other variable is recorded and extrapolated back to the time at which the step was applied, when the interfacial concentrations were not yet depleted. In the other class of method the transport of the reacting species is enhanced by convection. If the geometry of the system is sufficiently simple, the mass transport equations can be solved, and the surface concentrations calculated. The interpretation becomes complicated if several reactions take place simultaneously. Since the measured current gives only the sum of the rate of all charge-transfer reactions, the elucidation of the reaction mechanism and the measurement of several rate constants becomes an art. A number of tricks can be used, such as complicated potential or current programs, auxiliary electrodes, etc., which work for special cases. There are several good books on the classical electrochemical techniques. Here we give a brief outline of the most important methods. We mostly restrict ourselves to the study of simple reactions, but will consider one example in which the charge-transfer reaction is preceded by a chemical reaction. The measurement of current and potential provides no direct information about the microscopic structure of the interface, though a clever experimentalist may make some inferences.
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Schmickler, Wolfgang. "The double layer in the absence of specific adsorption." In Interfacial Electrochemistry. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195089325.003.0024.

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One of the fundamental problems in electrochemistry is the distribution of the potential and of the particles at the interface. Here we will expand on the subject of Chapter 3, and consider the interface between a metal and an electrolyte solution in the absence of specific adsorption. Until about 1980 a simple model of this interface prevailed, which was based on a particular interpretation of the interfacial capacity. The metal was assumed to be a perfect conductor in the classical sense, and hence a region of constant potential right up to the metal surface. As was pointed out in Chapter 3, the inverse capacity can be split into two terms, a Gouy-Chapman and a Helmholtz term: l/C = l/CGc + 1/CH. It was argued that these two terms pertain to two different regions in the solution: the space charge or diffuse double layer, which is already familiar to us, and the Stern or outer Helmholtz layer giving rise to the Helmholtz capacity. Since the latter does not depend on the concentration of the ions, the Stern layer was supposed to consist of a monolayer of solvent molecules adsorbed on the metal surface. The plane passing through the centers of these molecules was called the outer Helmholtz plane. Rather elaborate models were developed for the dielectric properties of this layer in order to explain Helmholtz capacity curves such as those shown in Fig. 3.3. This Gouy-Chapman-Stern model, as it was named after its main contributors, is a highly simplified model of the interface, too simple for quantitative purposes. It has been superseded by more realistic models, which account for the electronic structure of the metal, and the existence of an extended boundary layer in the solution. It is, however, still used even in current publications, and therefore every electrochemist should be familiar with it. In the remainder of this chapter we will present elements of modern double-layer theory. Two phases meet at this interface: the metal and the solution. We will consider each phase in turn.
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Schmickler, Wolfgang. "Selected experimental results for electron-transfer reactions." In Interfacial Electrochemistry. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195089325.003.0013.

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Innumerable experiments have been performed on both inner- and outer-sphere electron-transfer reactions. We do not review them here, but present a few results that are directly relevant to the theoretical issues raised in the preceding chapters. The Butler-Volmer equation (5.10) predicts that for |η| > kT/e0 a plot of the logarithm of the current versus the applied potential (Tafel plot) should result in a straight line, whose slope is determined by the transfer coefficient α. Because of the dual role of the transfer coefficient (see Section 5.2), it is important to verify that the transfer coefficient obtained from a Tafel plot is independent of temperature. We shall see later that proton- and ion-transfer reactions often give straight lines in Tafel plots, too, but the apparent transfer coefficient obtained from these plots can depend on the temperature, indicating that these reactions do not obey the Butler-Volmer law. In order to test the temperature independence of the transfer coefficient, Curtiss et al. investigated the kinetics of the Fe2+/Fe3+ reaction on gold in a pressurized aqueous solution of perchloric acid over a temperature range from 25° to 75°C. In the absence of trace impurities of chloride ions, this reaction proceeds via an outer sphere mechanism with a low rate constant (k0 ≈ 10-5 cm s-1 at room temperature). Figure 8.1 shows the slope of their Tafel plots, d(lni)/dη, as a function of the inverse temperature 1/T. The Butler-Volmer equation predicts a straight line of slope αe0/k, which is indeed observed. Over the investigated temperature range both the transfer coefficient and the energy of activation are constant: α = 0.425 ± 0.01 and Eact = 0.59± 0.01 eV at equilibrium, confirming the validity of the Butler-Volmer equation in the region of low overpotentials, from which the Tafel slopes were obtained. The phenomenological derivation of the Butler-Volmer equation is based on a linear expansion of the Gibbs energy of activation with respect to the applied overpotential. At large overpotentials higher-order terms are expected to contribute, and a Tafel plot should no longer be linear.
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"Electrochemical Behaviour of Transition Metal Complexes." In Inorganic Electrochemistry Theory, Practice and Application, 248–334. 2nd ed. The Royal Society of Chemistry, 2011. http://dx.doi.org/10.1039/bk9781849730716-00248.

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Chapter 6 moves inside the wide world of metal complexes bearing disparate ligands to detect their electron transfer activity. The multiple applicative examples here cited indicate the proper way to carry out the electrochemical characterization of the different oxidation states of a metal complex in order to complete their identification by spectroscopic techniques or to use the proper chemical agents to prepare large-scale metal complexes in different oxidation states.
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Conference papers on the topic "Heme electrochemistry"

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Hathiramani, D., R. Vaßen, D. Stöver, and R. J. Damani. "Comparison of Atmospheric Plasma Sprayed Anode Layers for SOFCs Using Different Feedstock." In ITSC2006, edited by B. R. Marple, M. M. Hyland, Y. C. Lau, R. S. Lima, and J. Voyer. ASM International, 2006. http://dx.doi.org/10.31399/asm.cp.itsc2006p0421.

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Abstract Atmospheric plasma spraying is a cost effective way to produce SOFC components. Doing so, sinter steps can be avoided, which is essential once a metallic support is used for the SOFC. Several properties are required regarding the micro structure of an optimized anode layer. Here gas permeability, electrochemistry, electronic conductivity, coefficient of thermal expansion as well as thermal shock resistance has to be considered. Different types of powder feedstock were investigated to develop an atmospheric plasma sprayed anode layer: (i) NiO or Ni together with YSZ as starting materials, (ii) agglomerates in which NiO and YSZ are already mixed on a sub-micrometer range, (iii) blended NiO/YSZ powder, (iv) separate injection of the individual NiO and YSZ powders, respectively into the plasma by two separate powder lines. The performance of APS anodes are measured in single fuel cell tests. Anode layers sprayed by a separate injection of the individual NiO and YSZ powders into the plasma show the best results.
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Magin, Richard L., and Dumitru Baleanu. "NMR Measurements of Anomalous Diffusion Reflect Fractional Order Dynamics." In ASME 2007 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/detc2007-34224.

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Diffusion weighted MRI is often used to detect and stage neurodegenerative, malignant and ischemic diseases. The correlation between developing pathology and localized diffusion measurements relies on the design of selective phase encoding pulses that alter the intensity of the acquired signal according to biophysical models of spin diffusion in tissue. The most common approach utilizes a bipolar or Stejskal-Tanner gradient pulse sequence to encode the apparent diffusion coefficient as an exponential, multi-exponential or stretched exponential function of experimentally-controlled parameters. Several studies have investigated the ability of the stretched exponential to provide an improved fit to diffusion-weighted imaging data. These results were recently analyzed by establishing a direct link between water diffusion, as measured using NMR, and fractal structural models of tissues. In this paper we suggest an alternative description for stretched exponential behavior that reflects fractional order dynamics of a generalized Bloch-Torrey equation in either space or time. Such generalizations are the basis for similar anomalous diffusion phenomena observed in optical spectroscopy, polymer dynamics and electrochemistry. Here we demonstrate a correspondence between the detected NMR signal and anomalous diffusional dynamics of water through the Riesz fractional order space derivative and the Caputo form of the fractional order Riemann-Liouville time derivative.
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Chen, Kok Hao, and Jong Hyun Choi. "DNA Oligonucleotide-Templated Nanocrystals: Synthesis and Novel Label-Free Protein Detection." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-11958.

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Semiconductor and magnetic nanoparticles hold unique optical and magnetic properties, and great promise for bio-imaging and therapeutic applications. As part of their stable synthesis, the nanocrystal surfaces are usually capped by long chain organic moieties such as trioctylphosphine oxide. This capping serves two purposes: it saturates dangling bonds at the exposed crystalline lattice, and it prevents irreversible aggregation by stabilizing the colloid through entropic repulsion. These nanocrystals can be rendered water-soluble by either ligand exchange or overcoating, which hampers their widespread use in biological imaging and biomedical therapeutics. Here, we report a novel scheme of synthesizing fluorescent PbS and magnetic Fe3O4 nanoparticles using DNA oligonucleotides. Our method of PbS synthesis includes addition of Na2S to the mixture solution of DNA sequence and Pb acetate (at a fixed molar ratio of DNA/S2−/Pb2+ of 1:2:4) in a standard TAE buffer at room temperature in the open air. In the case of Fe3O4 particle synthesis, ferric and ferrous chloride were mixed with DNA in DI water at a molar ratio of DNA/Fe2+/Fe3+ = 1:4:8 and the particles were formed via reductive precipitation, induced by increasing pH to ∼11 with addition of ammonium hydroxide. These nanocrystals are highly stable and water-soluble immediately after the synthesis, due to DNA termination. We examined the surface chemistry between oligonucleotides and nanocrystals using FTIR spectroscopy, and found that the different chemical moieties of nucleobases passivate the particle surface. Strong coordination of primary amine and carbonyl groups provides the chemical and colloidal stabilities, leading to high particle yields (Figure 1). The resulting PbS nanocrystals have a distribution of 3–6 nm in diameter, while a broader size distribution is observed with Fe3O4 nanoparticles as shown in Figure 1b and c, respectively. A similar observation was reported with the pH change-induced Fe3O4 particles of a bimodal size distribution where superparamagnetic and ferrimagnetic magnetites co-exist. In spite of the differences, FTIR measurements suggest that the chemical nature of the oligonucleotide stabilization in this case is identical to the PbS system. As a particular application, we demonstrate that aptamer-capped PbS QD can detect a target protein based on selective charge transfer, since the oligonucleotide-templated synthesis can also serve the additional purpose of providing selective binding to a molecular target. Here, we use thrombin and a thrombin-binding aptamer as a model system. These QD have diameters of 3∼6 nm and fluoresce around 1050 nm. We find that a DNA aptamer can passivate near IR fluorescent PbS nanocrystals, rendering them water-soluble and stable against aggregation, and retain the secondary conformation needed to selectively bind to its target, thrombin, as shown in Figure 2. Importantly, we find that when the aptamer-functionalized nanoparticles binds to its target (only the target), there is a highly systematic and selective quenching of the PL, even in high concentrations of interfering proteins as shown in Figure 3a and b. Thrombin is detected within one minute with a detection limit of ∼1 nM. This PL quenching is attributed to charge transfer from functional groups on the protein to the nanocrystals. A charge transfer can suppress optical transition mechanisms as we observe a significant decrease in QD absorption with target addition (Figure 3c). Here, we rule out other possibilities including Forster resonance energy transfer (FRET) and particle aggregation, because thrombin absorb only in the UV, and we did not observe any significant change in the diffusion coefficient of the particles with the target analyte, respectively. The charge transfer-induced photobleaching of QD and carbon nanotubes was observed with amine groups, Ru-based complexes, and azobenzene compounds. This selective detection of an unlabeled protein is distinct from previously reported schemes utilizing electrochemistry, absorption, and FRET. In this scheme, the target detection by a unique, direct PL transduction is observed even in the presence of high background concentrations of interfering negatively or positively charged proteins. This mechanism is the first to selectively modulate the QD PL directly, enabling new types of label free assays and detection schemes. This direct optical transduction is possible due to oligonucleotidetemplated surface passivation and molecular recognition. This chemistry may lead to more nanoparticle-based optical and magnetic probes that can be activated in a highly chemoselective manner.
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