Dissertations / Theses on the topic 'Implantable biosensors'

The goal for this thesis was to apply electrospun biomimetic coatings on implantable glucose biosensors and test their efficacy as mass-transport limiting and tissue engineering membranes, with special focus on achieving reliable and long sensing life-time for biosensors when implanted in the body. The 3D structure of electrospun membranes provides the unique combination of extensively interconnected pores, large pore volumes and mechanical strength, which are anticipated to improving sensor sensitivity. Their structure also mimics the 3D architecture of natural extracellular matrix (ECM), which is exploited to engineer tissue responses to implants. A versatile vertical electrospinning setup was built in our workshop and used to electrospin single polymer - Selectophore™ polyurethane (PU) and two polymer (coaxial) – PU and gelatin (Ge) fibre membranes. Extensive studies involving optimization of electrospinning parameters (namely solvents, polymer solution concentration, applied electric potential, polymer solution feed flow rate, distance between spinneret and collector) were carried out to obtain electrospun membranes having tailorable fibre diameters, pore sizes and thickness. The morphology (scanning electron microscopy (SEM) and optical microscopy), fibre diameter (SEM), porosity (bubble point and gravimetry methods), hydrophilicity (contact angle), solute diffusion (biodialyzer) and uniaxial mechanical properties (tensile tester) were used to characterize certain shortlisted electrospun membranes. Static and dynamic collector configurations for electrospinning fibres directly on sensor surface were optimized of which the dynamic collections system helped achieve snugly fit membranes of uniform thickness on the entire surface of the sensor. The biocompatibility and the in vivo functional efficacy of electrospun membranes off and on glucose biosensors were evaluated in rat subcutaneous implantation model. Linear increase in thickness of electrospun membranes with increasing electrospinning time was observed. Further, the smaller the fibre diameter, smaller was the pore size and higher was the fibre density (predicted), the hydrophilicity and the mechanical strength. Very thin membranes showed zero-order (Fickian diffusion exponent ‘n’ ~ 1) permeability for glucose transport. Increasing membrane thickness lowered ‘n’ value through non-Fickian towards Fickian (‘n’ = 0.5) diffusion. Thin electrospun PU membranes (~10 μm thick) did not affect, while thicknesses between 20 and 140 μm all decreased sensitivity of glucose biosensor by about 20%. PU core - Ge shell coaxial fibre membranes caused decrease in ex vivo sensitivity by up to 40%. The membranes with sub-micron to micron sized pore sizes functioned as mass-transport limiting membranes; but were not permeable to host cells when implanted in the body. However, PU-Ge coaxial fibre membranes, having <2 μm pore sizes, were infiltrated with fibroblasts and deposition of collagen in their pores. Such tissue response prevented the formation of dense fibrous capsule around the implants, which helped improve the in vivo sensor sensitivity. To conclude, this study demonstrated that electrospun membrane having tailorable fibre diameters, porosity and thickness, while having mechanical strength similar to the natural soft tissues can be spun directly on sensor surfaces. The membranes can function as mass-transport limiting membranes, while causing minimal or no effect on sensor sensitivity. With the added bioactive Ge surfaces, evidence from this study indicates that reliable long-term in vivo sensor function can be achieved.

Energy harvesting is identified as a promising alternative solution for powering implantable biosensors. It can completely replace the batteries, which are introducing many limitations, and it enables the development of self-powered implantable biosensors. An interface circuit is necessary to correct for differences in the voltage and power levels provided by an energy harvesting device from one side, and required by biosensor circuits from another. This thesis investigates the available energy harvesting sources within the human body, selects the most suitable one and proposes the power management unit (PMU), which serves as an interface between a harvester and biosensor circuits. The PMU targets the efficient power transfer from the selected source to the implantable biosensor circuits. Based on the investigation of potential energy harvesting sources, a thermoelectric energy harvester is selected. It can provide relatively high power density of 100 μW/cm2 at very low temperature difference available in the human body. Additionally, a thermoelectric energy harvester is miniature, biocompatible, and it has an unlimited lifetime. A power management system architecture for thermoelectric energy harvesters is proposed. The input converter, which is the critical block of the PMU, is implemented as a boost converter with an external inductor. A detailed analysis of all potential losses within the boost converter is conducted to estimate their influence on the conversion efficiency. The analysis showed that the inevitable conduction and switching losses can be reduced by the proper sizing of the converter’s switches and that the synchronization losses can be almost completely eliminated by an efficient control circuit. Additionally, usually neglected dead time losses are proved to have a significant impact in implantable applications, in which they can reduce the efficiency with more than 2%. An ultra low power control circuit for the boost converter is proposed. The control is utilizing zero-current switching (ZCS) and zero-voltage switching (ZVS) techniques to eliminate the synchronization losses and enhance the efficiency of the boost converter. The control circuit consumes an average power of only 620 nW. The boost converter driven by the proposed control achieves the peak efficiency higher than 80% and can operate with harvested power below 5 μW. For high voltage conversion ratios, the proposed boost converter/control combination demonstrates significant efficiency improvement compared to state-of-the-art solutions.<br><p>QC 20150413</p>

Energy harvesting is identified as an alternative solution for powering implantable biosensors. It can potentially enable the development of self-powered implants if the harvested energy is properly handled. This development implies that batteries, which impose many limitations, are replaced by miniature harvesting devices. Customized interface circuits are necessary to correct for differences in the voltage and power levels provided by harvesting devices from one side, and required by biosensor circuits from another. This thesis investigates the available harvesting sources within the human body, proposes various methods and techniques for designing power-efficient interfaces, and presents two CMOS implementations of such interfaces. Based on the investigation of suitable sources, this thesis focuses on glucose biofuel cells and thermoelectric harvesters, which provide appropriate performance in terms of power density and lifetime. In order to maximize the efficiency of the power transfer, this thesis undertakes the following steps. First, it performs a detailed analysis of all potential losses within the converter. Second, in relation to the performed analysis, it proposes a design methodology that aims to minimize the sum of losses and the power consumption of the control circuit. Finally, it presents multiple design techniques to further improve the overall efficiency. The combination of the proposed methods and techniques are validated by two highly efficient energy harvesting interfaces. The first implementation, a thermoelectric energy harvesting interface, is based on a single-inductor dual-output boost converter. The measurement results show that it achieves a peak efficiency of 86.6% at 30 μW. The second implementation combines the energy from two sources, glucose biofuel cell and thermoelectric harvester, to accomplish reliable multi-source harvesting. The measurements show that it achieves a peak efficiency of 89.5% when the combined input power is 66 μW.<br>Energiskörd har identifierats som en alternativ lösning för att driva inplanterbara biosensorer. Det kan potentiellt möjliggöra utveckling av själv-drivna inplanterbara biosensorer. Denna utveckling innebär att batterier, som sätter många begränsningar, ersätts av miniatyriserade energiskördsenheter. Anpassade gränssnittskretsar är nödvändiga för att korrigera för de skillnader i spänning och effektnivå som produceras av de energialstrande enheterna, och de som krävs av biosensorkretsarna. Denna avhandling undersöker de tillgängliga källorna för energiskörd i den mänskliga kroppen, föreslår olika metoder och tekniker för att utforma effektsnåla gränssnitt och presenterar två CMOS-implementeringar av sådana gränssnitt. Baserat på undersökningen av lämpliga energiskördskällor, fokuserar denna avhandling på glukosbiobränsleceller och termoelektriska energiskördare, som har lämpliga prestanda i termer av effektdensitet och livstid. För att maximera effektiviteten hos effektöverföringen innehåller denna avhandling följande steg. Först görs en detaljerad analys av alla potentiella förluster inom boost-omvandlare. Sedan föreslår denna avhandling en designmetodik som syftar till att maximera den totala effektiviteten och effektförbrukningen. Slutligen presenterar den flera designtekniker för att ytterligare förbättra den totala effektiviteten. Kombinationen av de föreslagna metoderna och teknikerna är varierade genom två högeffektiva lågeffekts energigränssnittskretsar. Den första inplementeringen är ett termoelektriskt energiskördsgränssnitt baserat på en induktor, med dubbla utgångsomvandlare. Mätresultaten visar att omvandlaren uppnår en maximal effektivitet av 86.6% vid 30 μW. Det andra genomförandet kombinerar energin från två källor, en glukosbiobränslecell och en termoskördare, för att åstadkomma en tillförlitlig multi-källas energiskördslösning. Mätresultaten visar att omvandlaren uppnår en maximal effektivitet av 89.5% när den kombinerade ineffekten är 66 μW.<br><p>QC 20170508</p><br>Mi-SoC

Identification, monitoring and quantification of biomolecules in the CNS is a field of growing interest for identifying biomarkers of neurological diseases. In this thesis, silicon needle-shaped multi-molecules sensing microprobes were developed. Our microelectrode array design comprises a needle length of 6mm with 100x50 µm2 cross-section bearing three platinum electrodes with a size of 40x200 µm and 200µm spacing between them. We have used these microprobes for simultaneous glucose and lactate monitoring, using the third electrode for control of non-specific current variations. Local microdroplet protein deposition on the electrode surface was achieved using a pneumatic picopump injection system. Enzyme immobilization on the electrode surface is a key step in microelectrode biosensor fabrication. We have developed a simple, low cost, non-toxic enzyme immobilization method employing poly(ethyleneglycol) diglycidyl ether (PEGDE). Successful biosensor fabrication was demonstrated with glucose oxidase, D-amino acid oxidase, and glutamate oxidase. We found that these biosensors exhibited high sensitivity and short response time sufficient for observing biological events in vivo on a second-by-second timescale. PEGDE-based biosensors demonstrated an excellent long-term stability and reliably monitored changes in brain glucose levels induced by sequential administration of insulin and glucose solution. We then carried out a comparative study of five enzyme immobilization procedures commonly used in Neuroscience: covalent immobilization by cross-linking using glutaraldehyde, PEGDE, or a hydrogel matrix and enzyme entrapment in a sol-gel or polypyrrole-derived matrices. Enzymatic microelectrodes prepared using these different procedures were compared in terms of sensitivity, response time, linear range, apparent Michaelis-Menten constant, stability and selectivity. We conclude that PEGDE and sol-gel techniques are potentially promising procedures for in vivo laboratory studies. The comparative study also revealed that glutaraldehyde significantly decreased enzyme selectivity while PEGDE preserved it. The effects that immobilization can have on enzyme substrate specificity, produce dramatic consequences on glutamate detection in complex biological samples and in the CNS. Our biosensor's results were systematically controlled by HPLC or capillary electrophoresis. The highly selective PEGDE-based biosensors allowed accurate measurements glutamate concentrations in the anesthetized and awaked rats at physiological conditions and under pharmacological and electrical stimulations. The microfabricated multielectrodes based on silicon needles coupled to the simple, non-toxic and mild immobilization method based on PEGDE, open new possibilities for specific neurotransmitter detection in the central nervous system and the study of cell-cell communication in vivo.

Electroporation is the critical step in an electric field mediated drug or gene delivery protocol. Electroporation based protocols have been successfully demonstrated in cancer clinical trials, however, its impact in other applications is still under investigation. A significant roadblock to long term functioning of implantable biosensors in vivo is the tissue reaction in the form of fibrous encapsulation that results in reduced transport to the sensing element of the biosensor. In vivo gene electroporation has a great potential as a means to modify the transport properties of tissues in the proximity of the sensing element of implantable biosensors. This dissertation examines two postulated electroporation based strategies to modify tissue for enhanced performance of an implantable biosensor. In the first, the implantation protocol is modified to accommodate in vivo electroporation. In the second strategy, the the modification is applied post implantation. This post-implantation in vivo electroporation application requires that electric energy be delivered at the site of electroporation close to the biosensor while minimizing effects far from such site. A novel method, focusing electric fields, developed for this purpose is presented. A theoretical framework as well as in vitro and in vivo experiments are provided as the introduction to the method and in support of its potential as the basis of a viable technology.

Diabetes is a chronic metabolic disorder whereby the body loses its ability to maintain normal glucose levels. Despite of development of implantable glucose sensors in long periods, none of the biosensors are capable of continuously monitoring glucose levels during long-term implantation reliably. Progressive loss of sensor function occurs due in part to biofouling and to the consequences of a foreign body response such as inflammation, fibrosis, and loss of vasculature. In order to improve the function and lifetime of implantable glucose sensors, a new 3D porous and bio-stable collagen scaffold has been developed to improve the biocompatibility of implantable glucose sensors. The novel collagen scaffold was crosslinked using nordihydroguaiaretic acid (NDGA) to enhance biostability. NDGA-treated collagen scaffolds were stable without any physical deformation in the subcutaneous tissue of rats for 4 weeks. The scaffold application does not impair the function of our sensor. The effect of the scaffolds on sensor function and biocompatibility was examined during long-term in vitro and in vivo experiments and compared with control bare sensors. The sensitivity of the short sensors was greater than the sensitivity of long sensors presumably due to less micro-motions in the sub-cutis of the rats. The NDGA-crosslinked scaffolds induced much less inflammation and retained their physical structure in contrast to the glutaraldehyde (GA)-crosslinked scaffolds. We also have developed a new dexamethasone (Dex, anti-inflammatory drug)-loaded poly(lactic-co-glycolic acid) (PLGA) microspheres/porous collagen scaffold composite for implantable glucose sensors. The composite system showed a much slower and sustained drug release than the standard microspheres. The composite system was also shown to not significantly affect the function of the sensors. The sensitivity of the sensors with the composite system in vivo remained higher than for sensors without the composites (no scaffold, scaffold without microspheres). Histology showed that the inflammatory response to the Dex-loaded composite was much lower than for the control scaffold. The Dex-loaded composite system might be useful to reduce inflammation to glucose sensors and therefore extend their function and lifetime.

L'objectif de cette thèse de doctorat est le développement de capteurs et d'algorithmes pour une meilleure surveillance de l'activité cardiaque dans un défibrillateur cardioverteur implantable sous-cutané (S-ICD), et plus précisément pour améliorer la spécificité de détection des tachyarythmies dangereuses telles que la tachycardie ventriculaire (TV) et la fibrillation ventriculaire (FV) dans le S-ICD. Deux schémas de détection TV/FV indépendants ont été développés dans ce but : l'un de nature électrophysiologique et l'autre hémodynamique. Le schéma de détection électrophysiologique repose sur un ECG spécial qui a été enregistré le long d'un dipôle «court» situé au-dessus du grand pectoral inférieur gauche. Ce dipôle court maximise le rapport R/T et le rapport signal/bruit chez 9 volontaires sains. En théorie, cela devrait réduire le risque de détections faussement positives de TV/ FV simplement en raison de la taille, de l'emplacement et de l'orientation du dipôle, indépendamment de toute autre méthode de traitement du signal. Le schéma de détection hémodynamique repose quant à lui sur les vibrations cardiaques enregistrées par deux prototypes de capteurs accéléromètres triaxiaux. Les vibrations cardiaques sous-cutanées mesurées ont été caractérisées, validées physiologiquement et optimisées via leur filtrage le long de bandes passantes spécifiques et leur projection le long d'un référentiel spécifique patient. Le premier algorithme au monde indépendant de détection de FV par vibration cardiaque a été développé en opérant sur ces signaux optimisés. Les mêmes prototypes d'accéléromètre se sont également avérés capables d'enregistrer des accélérations respiratoires et de détecter l'apnée. Enfin, un dernier prototype de sonde sous-cutanée composite, composé de trois électrodes, d'un accéléromètre bi-axial et de connecteurs d'appareil standard. Ce prototype est capable d'enregistrer l'ECG dipolaire court, les vibrations cardiaques et les accélérations respiratoires. Cette sonde prototype a été implantée dans un quatrième et dernier animal<br>The aim of this doctoral thesis was the development of sensors and algorithms for the improved monitoring of cardiac activity in the subcutaneous implantable cardioverter-defibrillator (SICD). More precisely, to improve the detection specificity of dangerous tachyarrhythmia such as ventricular tachycardia (VT) and ventricular fibrillation (VF). Two independent VT/VF detection schemes were developed for this: one electrophysiological in nature, and the other hemodynamic. The electrophysiological sensing scheme relied on a special ECG that was recorded along a short dipole located above the lower left pectoralis major. This short dipole maximised R/T ratio and signal-to-noise ratio in a total of 9 healthy volunteers. In theory, it will reduce the risk of false positive VT/VF detections simply by consequence of the dipole size, location, and orientation and independently of any further signal processing methods. The hemodynamic sensing scheme relied on cardiac vibrations recorded from two tri-axial accelerometer prototype sensors. These subcutaneous cardiac vibrations were characterised, physiologically validated, and optimised via their filtering along specific bandwidths and projection along a patient specific reference frame. The world’s first independent cardiac vibration VF detection algorithm was developed operating on these optimised signals. The same accelerometer prototypes were also shown to be able to record respiratory accelerations and detect apnoea. A final subcutaneous lead prototype was developed capable of recording the short dipole ECG, cardiac vibrations, and respiratory accelerations. It consisted of three electrodes, a bi-axial accelerometer, and industry-standard device connectors. The prototype lead was implanted in a fourth and final animal

Le fonctionnement du cerveau repose sur la libération de molécules telles que les neurotransmetteurs et les métabolites dans le milieu interstitiel. L’étude de ces molécules est donc primordiale afin de mieux comprendre leur rôle physiologique et pathologique. Pour cela, les biocapteurs enzymatiques implantables sont un outil prometteur de par leurs capacités de détection quantitative, en temps réel et dans les tissus profonds. En fonction des dimensions du biocapteur, l’impact de l’implantation peut avoir des conséquences considérables sur la composition chimique du fluide interstitiel. De plus, chaque implantation induit localement une réaction inflammatoire dite « réaction au corps étranger ». La réduction de ces réactions est indispensable afin d’obtenir des estimations plus précises de la concentration des molécules présentes. Dans ce sens, ce manuscrit exposera deux voies de réduction de l’impact lésionnel dû à l’implantation de biocapteurs. Tout d’abord, il sera présenté la miniaturisation de biocapteurs enzymatiques jusqu’à des diamètres externes inférieurs à 15 µm. Et il sera démontré in vivo que ces biocapteurs ultra miniaturisés ont le potentiel d’être implantés dans le cerveau sans induire de dommages détectables aux tissus et aux vaisseaux sanguins. Ensuite, le développement d’une microsonde fabriquée à l’aide des technologies MEMS couplant une détection électrochimique et optique sera introduit dans le cadre du suivi du fluide interstitiel péri- et intratumoral de glioblastomes modifiés pour émettre de la fluorescence. En intégrant deux types de détection sur une unique micro-aiguille, cette microsonde permet de réduire le nombre d’implantations. Ces deux voies de miniaturisation ouvrent la possibilité de suivre la composition chimique du fluide interstitiel de manière moins invasive, et donc de mieux préserver la physiologie des tissus étudiés dans le cerveau<br>Brain function is based on the release of molecules such as neurotransmitters and metabolites into the interstitial fluid. The study of these molecules is essential to better understand their physiological and pathological role. For this purpose, implantable enzymatic biosensors are a promising tool because of their quantitative, real-time and deep tissue detection abilities. Depending on the dimensions of the biosensor, the impact of implantation may have considerable consequences on the chemical composition of the interstitial fluid. In addition, each implantation induces a local inflammatory reaction called "foreign body reaction". The reduction of these reactions is crucial in order to provide more accurate estimations of molecules concentrations present in the interstitial fluid. In this sense, this manuscript will expose two ways of reducing the lesional impact due to the implantation of biosensors. First of all, it will be presented the miniaturization of enzymatic biosensors up to external diameters less than 15 µm. And it will be demonstrated in vivo that these ultra miniaturized biosensors have the potential to be implanted in the brain without inducing detectable damage to tissues and blood vessels. Then, the development of a microprobe fabricated using MEMS technologies combining electrochemical and optical detection will be introduced as part of the monitoring of peri- and intratumoral interstitial fluid from glioblastomes modified to fluoresce. By integrating two types of detection on a single micro-needle, this microprobe reduces the number of implantations. These two miniaturization approaches open up the possibility of following the chemical composition of the interstitial fluid in a less invasive way, and thus of better preserving the physiology of the tissues studied in the brain

Cocaine is a well-known, illegal, recreational drug that is addictive due to its effects on the mesolimbic reward pathway in the human body. Accurate and real-time measurement of the concentration of cocaine in the body as a function of time and physiological factors is a key requirement for the understanding of the use of this drug. Current methods for such measurements involve taking samples from the human body (such as blood, urine, and hair) and performing analytical chemistry tests on these samples. This techniques are relatively expensive, time consuming, and labor intensive. To address this issue, a new implantable sensor for the automated detection and measurement of the relative cocaine concentration is presented here. The device is more economical and provides for higher sampling frequencies than the current methods. The active sensor elements consist of piezoresistive microcantilever arrays, which are coated with an oligonucleotide-based aptamer, i.e. a short sequence of RNA with high affinity for specific target molecules, as the cocaine receptor. A Wheatstone bridge is used to convert the biosensor signal into an electronic signal. This signal is transmitted wireless at an operating frequency of 403.55 MHz, which complies with the US Medical Implant Communication System (MICS) FCC 47CFR Part 95. The limit of detection for the in vitro experiment is found to be 1 ng/ml. The device has successfully measured the relative concentration of cocaine upon implantation in the subcutaneous interstitial fluid of male Wistar rats.

碩士<br>國立臺灣大學<br>電機工程學研究所<br>96<br>In our study, preparation of the three-electrode biosensors used the MEMS technology. The three-electrode biosensors measured glucose and lactate using glucose oxidase (GOD) and lactate dehydrogenase (LDH). Biomedical and implantable sensor applications require stable, reproducible, reversible, and reliable miniaturized reference electrode , made of biocompatible materials. So the present study reports the application of protective membrane on the device, which exists both biocompatibility and permselectivity, and acts as a surface coating material for the outer layer of the Bio-sensor. For miniaturization of sensing system, we design a single-supply circuit. Thus, our study used difference protective membrane to assure the long-term stability of the Ag/AgCl reference electrode. From those results, we can know that reference electrode with polyurethane protective membrane is more stable than the one without protective membrane. In vivo performance, the sensor with polyurethane protective membrane can also work when implanted subcutaneously in a rat.

Thesis (Ph. D.)--University of Georgia, 2009.<br>Directed by William S. Kisaalita. Includes articles submitted to Talanta, Sensors and actuators B: chemical, Analytical and bioanalytical chemistry, and Biomaterials. Includes bibliographical references.

We aim to develop an implantable, optical neural imaging device by fabricating lasers and photodiodes onto a gallium arsenide substrate. Some studies suggest that lasers exhibit higher noise than light emitting diodes (LEDs) due to coherence effects – my studies aim to quantify this noise and to guide device development. To this end, I developed a model of a fluorescent imaging device which agreed with experiment. Noise analysis performed in phantom showed that laser sources exhibit temporal and spatial noise up to 10x higher than LED sources, and in vivo noise analysis also demonstrated this trend. I studied a neural injury model called cortical spreading depression in vitro in mouse brain slices and in vivo in the rat brain using laser and LED sources. Signal magnitudes in vitro are on the order of 10% and in vivo results are inconclusive. Future work will aim to reduce coherence related noise.

<p>As an increasingly prevalent chronic disease, diabetes represents one of the fastest growing health burdens to both the developed and developing world. In an effort to improve the management and treatment of diabetes, implantable sensors that continuously monitor glucose levels have become popular alternatives to patient-administered finger prick measurements of blood glucose. However, following implantation, the performance of these implants suffers from inaccurate and erratic readings that compromise their useful lives. As a result, implantable glucose sensors remain limited as a platform for the reliable management of diabetes. While the interaction between the sensor and its surrounding tissue has been posited as a culprit for erroneous in vivo sensor performance, there remains little evidence to support that theory.</p><p>This dissertation describes the effects that implant-associated tissue reactions have on implantable sensor function. Since tissue response to an implant changes over time, the overall effect of these tissue reactions is broken into two temporal phases: (1) the phase of weeks to months following implantation when a mature foreign body capsule is present around the sensor and (2) the phase of days to weeks immediately following sensor implantation when a provisional matrix of proteins and inflammatory cells envelops the sensor.</p><p>Late stage sensor responses to implantation are marked by both an attenuated sensor signal and a significant time lag relative to blood glucose readings. For this later stage of sensor response, a computational model of glucose transport through the interstitial space and foreign body capsule was derived and implemented. Utilizing physiologically relevant parameters, the model was used to mechanistically study how each constituent part of the capsular tissue could affect sensor response with respect to signal attenuation and lag. Each parameter was then analyzed using logarithmic sensitivity analysis to study the effects of different transport variables on both lag and attenuation. Results identified capsule thickness as the strongest determinant of sensor time lag, while subcutaneous vessel density and capsule porosity had the largest effects on attenuation of the sensor signal.</p><p>For the phase of early stage tissue response, human whole blood was used as a simple ex vivo experimental system. The impacts of protein accumulation at the sensor surface (biofouling effects) and cellular consumption of glucose in both the biofouling layer and in the bulk (metabolic effects) on sensor response were assessed. Medtronic Minimed SofSensor glucose sensors were incubated in whole blood, plasma diluted whole blood, and cell-free platelet poor plasma (PPP) to analyze the effects of different blood constituents on sensor function. Experimental conditions were then simulated using MATLAB to predict the relative impacts of biofouling and metabolic effects on the observed sensor responses. It was found that the physical barrier to glucose transport presented by protein biofouling did not hinder glucose movement to the sensor surface. Instead, glucose consumption by inflammatory cells was identified as the major culprit for generating poor sensor performance immediately following implantation.</p><p>Lastly, a novel, biomimetic construct was designed to mimic the in vivo 3D cellular setting around the sensor for the focused in vitro investigation of early stage effects of implantation on glucose sensor performance. Results with this construct demonstrate similar trends in sensor signal decline to the ex vivo cases described above, suggesting this construct could be used as an in vitro platform for assessing implantable glucose sensor performance.</p><p>In total, it may be concluded from this dissertation that instead of sensors "failing" in vivo, as is often reported, that different physiological factors mediate long term sensor function by altering the environment around the implant. For times immediately following implantation, sensor signals are mediated by the presence of inflammatory macrophages adhered on the surface. However, at longer times post-implantation, sensor signals are mediated not by the consumptive capacity of macrophages, but instead by the subcutaneous vessel density surrounding the sensor as well as the porosity and thickness of the foreign body capsule itself. Taken in concert, the results of this dissertation provide a temporal framework for outlining the effects of tissue response on sensor performance, hopefully informing more biocompatible glucose sensor designs in the future.</p><br>Dissertation

<div>Glutamate is the principal excitatory neurotransmitter in the central nervous system. As one of the most abundant neurotransmitters, glutamate plays an essential role in many processes of the central nervous system and beyond. As a result, any disruption that causes an abnormal glutamate level can significantly impact the central nervous system's neurological functions. Glutamate excitotoxicity is a neuropathology that persists in many neurodegenerative disorders such as Parkinson's and Alzheimer's disease as well as in the traumatic brain and spinal cord injuries. Thus, the ability to obtain precise information about the extracellular glutamate level in the living brain and spinal cord tissue may provide new insights into the fundamental understanding of glutamate in neurological disorders and neurophysiological phenomena.</div><div><br></div><div>Conventional bioanalytical techniques that characterize glutamate levels <i>in vivo</i> have a low spatiotemporal resolution that has impeded our understanding of this dynamic event. The electrochemical sensor has emerged as a promising solution that can satisfy the requirement for highly reliable and continuous monitoring methods with an excellent spatiotemporal resolution for the characterization of extracellular glutamate concentration. In this thesis, I present various amperometric biosensors fabricated using a simple direct ink writing technique for<i> ex vivo </i>and <i>in vivo</i> glutamate monitoring.</div><div><br></div><div>The amperometric biosensor is fabricated by immobilizing glutamate oxidase on nanocomposite electrodes made of platinum nanoparticles, multiwalled carbon nanotubes, and a conductive polymer. The biosensors demonstrate good sensitivity and selectivity that can be inserted into a spinal cord and measure extracellular glutamate concentration. Additionally, another type of glutamate biosensor is fabricated from commercially available activated carbon with platinum microparticles. We utilize astrocyte cell culture to demonstrate our biosensor's ability to monitor the glutamate uptake process. We also present a direct measurement of glutamate release from optogenetic stimulation in mouse primary visual cortex brain slides. </div><div><br></div><div>Moreover, we explore a new type of material, perovskite nickelate-Nafion heterostructure, to fabricate biosensors and measure glutamate inside the mouse brain. Finally, by utilizing the nanocomposite ink and direct ink writing technique, we also fabricate the gold-ruthenium non-enzymatic glucose biosensor. We apply a modified Butler-Volmer non-linear model to evaluate the impact of geometrical and chemical design parameters of non-enzymatic biosensor performance. </div><div><br></div>

博士<br>中原大學<br>生物醫學工程研究所<br>99<br>This thesis developed an implantable wireless glucose sensing system and studied its functionality in rats. The system includes an external controller for serving as a human-system interaction interface and an implant unit for electrochemically sensing glucose. The communications between the controller and the implant are through a pair of antenna (or coils) based on peer-to-peer radio frequency (RF) technology. The electric power of the implant is supplied by the controller by means of RF coupling. The commands issued from the controller to the implant and the glucose signals sent back from the electrochemical analyzer of the implant to the controller all rely on the wireless RF technology. To be able to utilize the implant in rats, the implant unit requires not only miniaturization but also hermetically packaging. The whole part of the implant unit was sealed with poly-dimethylsiloxane except for a mini-electrode set. It is self-developed and is a piece of silicon containing working, reference and counter electrodes. This work also focuses on reducing protein absorption on surface of the electrode set when it is implanted within the rats. The working electrode modified with various TPU concentrations for GOx immobilization was used to evaluate the impact of the protein absorption. The evaluation study was carried out in simulated interstitial fluid (interstitial fluid surrogate, ISF surrogate) by an AUTOLAB PGSTAT10. Results indicate that 30 mg/ml of TPU reduced protein absorption most effectively. The modified electrode exhibited excellent stability as well because the TPU retained approximately 100% of GOx activity for more than 21 days. How the performance of the entire implantable glucose sensing system is even important in this work. Hydrogen peroxide signal measurements by the developed system and AUTOLAB were performed to evaluate the signal detection resolution. Results indicate the resolutions of the developed system and AUTOLAB were 114 and &amp;lt; 9.7 nA, respectively. This implied the TPU membrane to be used with the developed glucose sensing system requires modifications. The experimental results indicate that the developed system can detect a distinguishable glucose current response from ISF surrogate by using a 20 mg/ml TPU membrane. This implantable glucose biosensor with a TPU membrane was subsequently implanted in normal and diabetic rats. The signal responses obtained from the study rats’ ISF exhibited a significant difference when the blood glucose level changed. A comparison of intravenous and ISF glucose levels revealed a 30 to 170 minutes delay.

Medical care has been significantly improved in recent years due to tremendous technological advancement in the field of CMOS technology. Among those improvements, integrated circuit design and sensing techniques have brought to the doctors more flexibility and accuracy of examinations of their patients. For example, a diabetic patient needs to visit a hospital on a regular basis for the examination and proper treatment. However, with the tremendous advancement in electronic technology, a patient can soon monitor his or her own blood glucose level at home or at office with an implantable sensor which can also trigger insulin pump attached to the body. The insulin delivery system can be precisely controlled by the electronics embedded in the implantable device.In this thesis, a low power integrated circuit for the implantable biosensor incorporating an on-chip FSK modulator is presented. This design has been fabricated using AMI 0.5-μm CMOS process available through MOSIS. The simulation and test results are also presented to verify its operation.

碩士<br>國立臺灣海洋大學<br>機械與機電工程學系<br>106<br>Tilapia, an economically important cultured fish in Taiwan, plays a significant role in the fisheries development. It has less tolerable attributes of cold in winter and common bacterial infections in summer. Measurements of the variation of fish blood glucose and lactate concentration is a useful index to observe the change of physiological conditions. In this study, we adopted enzyme method to developed enzymatic biofuel cells and mediator-type biosensor. Enzymatic biofuel cell that consists of a needle bioanode used for glucose dehydrogenase (GDH) and a gas-diffusion biocathode used for bilirubin oxidase (BOD). The assembled device for glucose oxidation was inserted into Tilapia, producing maximum current density 41 (µA/cm^2),open voltage 0.41V, maximum power density 6.3(µW/cm^2) at 22℃ and maximum current density 52 (µA/cm^2), maximum power density 8.6(µW/cm^2) at 15℃ in free-swimming fish in the aquarium. We developed a wireless biosensor system to monitor glucose and lactate concentration in Tilapia. The biosensor was used Pt-Ir wire as the working electrode and Ag/AgCl as the reference electrode. Glucose dehydrogenase and lactate oxidase were immobilized on the working electrode to be glucose biosensor and lactate biosensor respectively. The sensor was inserted into Tilapia in order to wirelessly monitor the glucose and lactate concentration in free-swimming fish.We confirmed that blood glucose levels increased from 40mg/dl to 90mg/dl and lactate levels decreased from 20mg/dl to 10mg/dl in the blood when the temperatures dropped from 20℃to 15℃ in the aquarium. We also monitored the concentrations of glucose and lactate in Tilapia when it was infected by Streptococcosis. The results confirmed that blood glucose concentration increased from 41mg/dl to 92mg/dl and lactate concentration increased from 20mg/dl to 39mg/dl in the blood. The concentration from the sensor gradually increased and decreased during the application of stress, which hinted that the stress was monitored by this system. Keywords: Tilapia, Glucose enzyme, Lactate enzyme, Blood, Streptococcosis , Electrochemical analyzer , Wireless potential

碩士<br>國立臺灣科技大學<br>化學工程系<br>105<br>In this research, we used the semiconductor manufacturing technique to fabricate implantable multi-electrode array microprobes and AutoCAD software to design masks. The process to prepare microprobes was divided into three parts, including formation of the specific pattern of platinum metal layer on the silicon wafer, etching of the specific insulation layer and defining the outline of microprobes. We have three kinds of microprobes designed on a 4-inch wafer, including 53 probes with 4 microelectrodes, 74 probes with 4 microelectrodes and 2 long electrodes, 37 probes with 6 microelectrodes. Each probe consists of electrode sites, channels, bonding pads. Additionally, the 4-electrode microprobes were smaller than the others with full length 13 mm, width 3 mm, probe tip width 132 μm, and platinum area size 140 μm × 30 μm; while the others were of the same size with full length 18 mm, width 3 mm, thickness 200 μm, probe tip width 150 μm, and platinum area size 200 μm × 50 μm. The appropriate pattern can be selected according to future applications. Moreover, we optimized parameters in each processing step (i.e. thermal oxidation, photolithography, thin film deposition, and etching) to miniaturize the size, reduce cost, and improve the production rate of multi-electrode array microprobes. Different from the traditional three-electrode system, we designed our microprobes as all-in-one biosensor probes. For example, silver/silver chloride can be deposited onto one of electrode sites to make a self-reference electrode, while others are responsible for the counter and working electrode. An all-in-one biosensor can be applied in implantable biological sensing and greatly enhance its applications, feasibility, and convenience. In the second part of this thesis, sensors abilities were tested. In detail, we modified the electrode surface with permselective polymer layers and glutamate oxidase layers to construct glutamate biosensors. For this study, our glutamate sensors have fast response time 3±2 s, wider linear detection range 20-500 μM, low detection limit 1.15±0.01 μM, and high sensitivity 190±7.5 nA·μM-1·cm-2. We have proposed a multi-electrode array glutmate biosensor probe with good sensing ability. The proposed all-in-one glutmate sensor microprobes could be applied for different kinds in vivo experiment in live rodents in the future.