360 research outputs found

    A new data analysis approach for an AgNPs-modified impedimetric bioelectronic tongue for dairy analysis

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    Producción CientíficaAn alternative approach to analyze complex matrices, such as milk, lies on multivariate description of the chemical composition of samples, where fingerprints for each sample are generated using data mining methods (Principal Component Analysis, PCA, and Supported Vector Machine). Electronic tongues (ET) hold substantial potential for the dairy industry as analytical tools due to their fast analysis. The purpose of this work was to create an impedimetric ET with an array of microelectrode sensors for application in the dairy industry. A sensor array with enhanced sensitivity and selectivity silver nanoparticles and enzymes were developed. Higher sensitivity was evident in the responses of this array to milk components of interest like glucose, galactose, lactose, and urea. PCA of the signals obtained using the optimized ET has allowed the discrimination of milks with different characteristics. SVM was used to stablish correlations between the signals obtained from the ET and the physicochemical parameters. Electrochemical Impedance Spectroscopy have also shown that the ET in combination with the equivalent circuits approach could be a potential tool for its further application in dairy analysis. Moreover, the study of milk samples confirmed the high cross-selectivity of the system which allowed the development of classification models and to stablish correlations between the ET and physicochemical parameters.MICINN-FEDER (PID2021-122365OB-I00) «Infraestructuras Red de Castilla y León (INFRARED)»Junta de Castilla y León - Consejería de Educación - FEDER (VA275P18)Calidad Pascual farm (Aranda de Duero) (ALIVAC-IDI-20211051

    Flexible Label-Free Platinum and Bio-PET-Based Immunosensor for the Detection of SARS-CoV-2

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    The demand for new devices that enable the detection of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) at a relatively low cost and that are fast and feasible to be used as point-of-care is required overtime on a large scale. In this sense, the use of sustainable materials, for example, the bio-based poly (ethylene terephthalate) (Bio-PET) can be an alternative to current standard diagnostics. In this work, we present a flexible disposable printed electrode based on a platinum thin film on Bio-PET as a substrate for the development of a sensor and immunosensor for the monitoring of COVID-19 biomarkers, by the detection of L-cysteine and the SARS-CoV-2 spike protein, respectively. The electrode was applied in conjunction with 3D printing technology to generate a portable and easy-to-analyze device with a low sample volume. For the L-cysteine determination, chronoamperometry was used, which achieved two linear dynamic ranges (LDR) of 3.98-39.0 μmol L-1 and 39.0-145 μmol L-1, and a limit of detection (LOD) of 0.70 μmol L-1. The detection of the SARS-CoV-2 spike protein was achieved by both square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) by a label-free immunosensor, using potassium ferro-ferricyanide solution as the electrochemical probe. An LDR of 0.70-7.0 and 1.0-30 pmol L-1, with an LOD of 0.70 and 1.0 pmol L-1 were obtained by SWV and EIS, respectively. As a proof of concept, the immunosensor was successfully applied for the detection of the SARS-CoV-2 spike protein in enriched synthetic saliva samples, which demonstrates the potential of using the proposed sensor as an alternative platform for the diagnosis of COVID-19 in the future

    Cardiovascular health: from cardiomyocyte electrostimulation to miRNA detection

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    Current methods of cell culture where electrical stimulation is applied during culture require a wired connection to a power supply to generate an electric field with which to stimulate the cells. This method is intrusive in a lab setting and does not conveniently allow for traditional cell culture techniques during stimulation, hence it is frequently omitted from cell culture protocols. The aim of this work is to demonstrate a novel method of electrical stimulation of cardiomyocytes using wireless bipolar electrochemical techniques. The work describes the design and characterisation of a wireless bipolar electrode and wireless bipolar electrochemical cell to facilitate wireless bipolar electrostimulation. By using a wireless connection more versatile experiments can be conducted on cells in culture while mitigating the contamination risk of a traditional wired stimulation platform. Using a polypyrrole based conducting film doped with fibronectin molecules to facilitate the adherence and growth of cardiomyocytes on the bipolar electrode surface. Cell culture on a conductive film opens the possibility of future applications in electroceuticals by providing a wireless platform to deliver and electric field to cells in culture. Demonstrating cell culture on conductive polymer with the application of electric fields allows for the study of healthy and disease cell populations in the presence of electrical stimuli. Biomarker monitoring during this work is important to characterise and understand the impact of stimuli on the cells in culture. As such, an electrochemical miRNA biosensor was also explored in this work. The assay was based on the detection of miRNA through hydrogen peroxide degradation. The assay was built of screen-printed electrodes as a method to characterise cell cultures. The ability to monitor biomarkers both in vitro and in vivo is important in generating an understanding of disease models and in the development of point-of-care testing capabilities

    The Development of Electrochemical Sensors and their Application in Real Biological Environments

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    Screen printed sensors and applications have been developed that utilise carbon/graphite working and counter electrodes and silver reference electrodes.The first sensor produced is a pH sensor where the working electrode hasbeen functionalised by spin coating a layer of DMSO-melanin which enablesit to become sensitive to changes in pH. This pH sensor was initially tested inreference buffer solutions where the sensitivity to pH was -49.79mV/pH±8.93over a range of pH4 to pH10. Further testing showed an improved sensitivityof -63mV/pH±4.79 over a range of pH5 to pH8 which is a biologically relevantrange. The DMSO-melanin pH sensor was tested in culturing mediathat had been inoculated and live bacteria were present where it was demonstrated to maintain sensitivity to pH in the presence of bacteria suggesting that it is suitable for the use in bacterial culturing applications. It was observed that signal measured depends on the type of culturing media used sotherefore the type of culturing media must be known in advance of testingand a standard curve for each type of media being tested must be establishedbefore testing. Testing the DMSO-melanin pH sensors with blood samplesin a preclinical model revealed challenges in obtaining repeatable results inblood samples. Subsequent investigation into this indicated that substanceswithin the blood interfere with the signal that is measured by the sensor, inparticular NaCl, KCl and MgCl2. This work also produced a nonfunctionalisedcarbon/graphite screen printed electrode that was able to accuratelymeasure the concentration of Lactobacillus casei bacteria in culturing mediasolutions using square wave voltammetry. The shape of the voltammogramsmeasured was different when cultures of Escherichia coli and Saccharomycescerevisiae were tested suggesting that there might be potential useful applications involving this technique to identify characteristics of microbiota(such as domain, species, Gram type and quantity) based on the measuredvoltammograms. However further research on an expanded number of differentprokaryotic and eukaryotic microorganisms is needed to confirm whethersuch applications are possible

    Organic electrochemical transistors with PVA hydrogels/PEDOT:PSS channel

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    Most organic electrochemical transistor (OECT)-based biosensors currently rely solely on the generation of electronic signals upon sensor-analyte interaction which has limited the range of analytes to those with distinct electronic properties or those that rely on specific biological materials with poor environmental stability, such as redox enzymes and antibodies. The development of durable stimuli-responsive hydrogels, which exhibit changes in ionic conductivity upon interacting with specific analytes, has significantly expanded the potential for ionic-based sensing as an alternative to electronic-based sensing. Although OECTs are suitable for measuring ionic signals, there have been only a few instances where these materials have been utilized within an OECT platform. This study investigates the applicability of OECTs for ionic-based sensing using poly(vinyl alcohol) (PVA) hydrogels and PEDOT:PSS based OECTs. Through varying macromer percentage alone, a set of hydrogels was fabricated that mimics the network properties seen in complex analyte-responsive systems. These hydrogels offer a cheap alternative, without the use of biorecognition elements, for probing OECT sensitivity to ionic signals. A system based on four electrode impedance spectroscopy was also developed to independently measure their ionic conductivity, with preliminary results consistent with values reported in literature. To enhance device reproducibility and improve compatibility with hydrogel deposition, a novel OECT geometry was designed. This involved incorporating larger features such as wider channels and thicker electrode contacts to minimize fabrication artifacts which ultimately improved OECT transconductance. Additionally, the impact of 3 direct polymerization of hydrogels on PEDOT:PSS was explored using Raman spectroscopy. The findings revealed that a high degree of adherence between the hydrogel and PEDOT:PSS may significantly reduce the dedoping capacity of PEDOT:PSS. Overall, this work represents a valuable first step in exploring the suitability of OECTs to ionic flow based sensing using hydrogels.Open Acces

    Microenvironment Restruction of Emerging 2D Materials and their Roles in Therapeutic and Diagnostic Nano-Bio-Platforms

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    Engineering advanced therapeutic and diagnostic nano-bio-platforms (NBPFs) have emerged as rapidly-developed pathways against a wide range of challenges in antitumor, antipathogen, tissue regeneration, bioimaging, and biosensing applications. Emerged 2D materials have attracted extensive scientific interest as fundamental building blocks or nanostructures among material scientists, chemists, biologists, and doctors due to their advantageous physicochemical and biological properties. This timely review provides a comprehensive summary of creating advanced NBPFs via emerging 2D materials (2D-NBPFs) with unique insights into the corresponding molecularly restructured microenvironments and biofunctionalities. First, it is focused on an up-to-date overview of the synthetic strategies for designing 2D-NBPFs with a cross-comparison of their advantages and disadvantages. After that, the recent key achievements are summarized in tuning the biofunctionalities of 2D-NBPFs via molecularly programmed microenvironments, including physiological stability, biocompatibility, bio-adhesiveness, specific binding to pathogens, broad-spectrum pathogen inhibitors, stimuli-responsive systems, and enzyme-mimetics. Moreover, the representative therapeutic and diagnostic applications of 2D-NBPFs are also discussed with detailed disclosure of their critical design principles and parameters. Finally, current challenges and future research directions are also discussed. Overall, this review will provide cutting-edge and multidisciplinary guidance for accelerating future developments and therapeutic/diagnostic applications of 2D-NBPFs

    Cyclodextrin Impedimetric Biosensors for the Detection of Hydrophobic Metabolites

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    Sepsis is a complicated medical emergency and critically ill patients suffering from infectious diseases are at a high risk for developing and dying from sepsis. According to a recent (2019) cohort study from six United States hospitals, suboptimal care (e.g., delay in antibiotics, inappropriate antibiotic therapy) is responsible for 22.7 % of in-hospital sepsis-associated deaths. In September 2020, the World Health Organization called on the scientific community to develop rapid, effective, and affordable tools to improve diagnosis, surveillance, and treatment of sepsis. Our long-term goal throughout this project is to develop a cyclodextrin (CD) impedimetric tongue that can provide early warning of sepsis by continuous monitoring the course of the disease and real-time profiling of urine samples in hospitalized patients. The cyclodextrin impedimetric tongue will also enable healthcare professionals to closely monitor the patients, predict sensitivity and resistance to therapies, decide about the dose of medications, and develop more effective personalized therapies for septic patients.Cyclodextrins, oligosaccharides with a hydrophobic cavity and a hydrophilic surface, are promising biorecognition elements in development of reusable impedimetric tongues. Cyclodextrins can semi-selectively detect different metabolites in the solutions through hydrophobic interactions, Van der Waals forces, and hydrogen bonding. The first aim of this thesis was to develop the first reusable nanostructured cyclodextrin platform using αCD and a weak surface αCD mediator: polyethylene glycol (PEG). To create the Gold-PEG:αCD surface, gold surface was modified with PEG via thiol-gold chemistry and the PEG support enabled reversible immobilization of αCD. We investigated the performance of this platform for detection of a model hydrophobic analyte, trans-resveratrol. Non-faradaic electrochemical impedance spectroscopy (EIS) measurement of the surface suggested that when αCD surfaces are introduced to a solution containing trans-resveratrol, αCD molecules leave the PEG support to interact with trans-resveratrol in the solution. After use, the surface could be regenerated by reloading of αCD. The second aim of this thesis was to improve the stability and reusability of cyclodextrin sensing platform by replacing gold-thiol bonds with carbon-carbon covalent bonds between glassy carbon (GC) and 4-carboxyphenyl diazonium salt. The GC-carboxyphenyl was modified with polypropylene glycol (PPG) through EDC/NHS chemistry. The PPG surface was then loaded with βCD. We used the GC-carboxyphenyl-PPG:βCD surface for sensitive detection of cortisol in biofluids (i.e., urine and saliva), and demonstrated the successful regeneration and reuse of the GC-carboxyphenyl-PPG:βCD surface for ten times. Finally, we employed sensitive, stable, and reusable cyclodextrin nanostructured surfaces to develop the first-generation cyclodextrin impedimetric tongue for separation and classification of four classes of bioanalytes including creatinine, cortisol, glucose, and fumarate. We applied linear discriminant analysis (LDA) to integrate and map the data, and by using the normalized changes in imaginary capacitance of three cyclodextrin surfaces (γCD at 79 Hz, hydroxypropyl-βCD at 0.25 Hz, and hydroxypropyl-γCD at 63.34 Hz), we achieved the 5-fold cross validation accuracy of 69%. Different methods of data preparation, EIS signal processing, and determining the characteristic frequencies of different analytes and single frequencies of cyclodextrin surfaces affect the accuracy of the impedimetric tongue. By optimizing these parameters, we can improve the performance and accuracy of the impedimetric tongue and apply this device for point of need applications

    Nanostructured biosensors with DNA-based receptors for real-time detection of small analytes

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    In zahlreichen lebenswichtigen Bereichen haben sich Biosensoren als unverzichtbare Messgeräte erwiesen. Der Nachweis von spezifischen Molekülen im Körper für eine frühzeitige Krankheitserkennung erfordert empfindliche und zugleich zuverlässige Messmethoden. Ein rasantes Fortschreiten im Bereich der Nanotechnologie führt dabei zur Entwicklung von Materialien mit neuen Eigenschaften, und damit verbunden, auch zu innovativen Anwendungsmöglichkeiten im Bereich der Biosensorik. Das Zusammenspiel von Nanotechnologie und Sensortechnik gewährleistet die Konstruktion von Sensoren mit empfindlicheren Nachweisgrenzen und kürzeren Reaktionszeiten. Die Option zur Integration und Miniaturisierung stellen daher einen erfolgreichen Einsatz in direkter Patientennähe in Aussicht, sodass Nanobiosensoren die Brücke zwischen Laborddiagnostik und Standardanwendungen schließen können. Die folgende Arbeit widmet sich der Anwendung von nanostrukturierten Biosensoren für einen empfindlichen und markierungsfreien Nachweis von Zielmolekülen. Ein Hauptaugenmerk liegt dabei auf der kontinuierlichen Messung von Biomarkern mit kompakten Auslesesystemen, die eine direkte Signalmeldung und somit eine Detektion in Echtzeit ermöglichen. Dies erfordert zunächst die sorgfältige Funktionalisierung von Sensoroberflächen mit geeigneten DNA-basierten Rezeptoren. Infolgedessen werden beispielhaft verschiedene Sensorsysteme, Analyten und Charakterisierungsmethoden vorgestellt sowie universelle Strategien für die erfolgreiche Konfiguration von Nanobiosensorplattformen präsentiert. Das erste Anwendungsbeispiel widmet sich einem plasmonischen Biosensor, bei dem vertikal ausgerichtete Gold-Nanoantennen Signale mittels sog. lokalisierter Oberflächenplasmonenresonanz (LSPR) erzeugen. Mit dem Sensor konnte erfolgreich die Immobilisierung, das nachträgliche Blocken sowie die anschließende Hybridisierung von DNA nachgewiesen werden. Mithilfe des LSPR-Sensors wurden gleichzeitig grundlegende Hybridisierungsmechanismen auf nanostrukturierten und planaren Oberflächen verglichen und damit verbunden die einzigartigen optischen Eigenschaften metallischer Nanostrukturen betont. In einem zweiten Anwendungsbeispiel misst ein elektrischer Biosensor kontinuierlich die Konzentration des Stressmarkers Cortisol im menschlichen Speichel. Der direkte, markierungsfreie Nachweis von Cortisol mit Silizium-Nanodraht basierten Feldeffekttransistoren (SiNW FET) wurde anhand zugrunde liegender Ladungsverteilungen innerhalb des entstandenen Rezeptor-Analyte-Komplexes bewertet, sodass ein Nachweis des Analyten innerhalb der sog. Debye-Länge ermöglicht wird. Die erfolgreiche Strategie zur Oberflächenfunktionalisierung im Zusammenspiel mit dem Einsatz von SiNW FETs auf einem tragbaren Messgerät wurde anhand des Cortisolnachweises im Speichel belegt. Ein übereinstimmender Vergleich der gemessenen Corisolkonzentrationen mit Werten, die mit einer kommerziellen Alternative ermittelt wurden, verdeutlichen das Potential der entwickelten Plattform. Zusammenfassend veranschaulichen beide vorgestellten Nanobiosensor-Plattformen die vielseitige und vorteilhafte Leistungsfähigkeit der Systeme für einen kontinuierlichen Nachweis von Biomarkern in Echtzeit und vorzugsweise in Patientennähe.:Kurzfassung I Abstract III Abbreviations and symbols V Content VII 1 Introduction 1 1.1 Scope of the thesis 4 1.2 References 6 2 Fundamentals 9 2.1 Biosensors 9 2.2 Influence of nanotechnology on sensor development 10 2.3 Biorecognition elements 12 2.3.1 Biorecognition element: DNA 13 2.3.2 Aptamers 14 2.3.3 Immobilization of receptors 15 2.4 Transducer systems 17 2.4.1 Optical biosensors - surface plasmon resonance 17 2.4.2 Electric Biosensors – Field-effect transistors (FETs) 21 2.5 Metal oxide semiconductor field-effect transistor - MOSFET 21 2.6 Summary 26 2.7 References 27 3 Materials and methods 33 3.1 Plasmonic biosensors based on vertically aligned gold nanoantennas 33 3.1.1 Materials 33 3.1.2 Manufacturing of nanoantenna arrays 34 3.1.3 Surface modification and characterization 35 3.1.4 Measurement setup for detection of analytes 38 3.2 SiNW FET-based real-time monitoring of cortisol 40 3.2.1 Materials 40 3.2.2 Manufacturing of silicon nanowire field effect transistors (SiNW FETs) 42 3.2.3 Integration of SiNW FETs into a portable platform 42 3.2.4 Biomodification and characterization of electronic biosensors SiNW FETs 42 3.2.5 Electric characterization of FETs 47 3.3 References 50 4 Plasmonic DNA biosensor based on vertical arrays of gold nanoantennas 51 4.1 Introduction - Optical biosensors operating by means of LSPR 53 4.2 Biosensing with vertically aligned gold nanoantennas 56 4.2.1 Sensor fabrication, characterization, and integration 56 4.2.2 Integration of microfluidics 58 4.2.3 Immobilization of probe DNA and backfilling 58 4.2.4 Hybridization of complementary DNA strands 62 4.2.5 Surface coverage and hybridization efficiency of DNA 69 4.2.6 Refractive index sensing 72 4.2.7 Backfilling and blocking 73 4.3 Summary 75 4.4 References 77 5 Label-free detection of salivary cortisol with SiNW FETs 83 5.1 Introduction 85 5.2 Design, integration, and performance of SiNW FETs into a portable platform 89 5.2.1 Structure and electrical characteristics of honeycomb SiNW FETs 89 5.2.2 Integration of SiNW FET into a portable measuring unit 91 5.2.3 Performance of SiNW FET arrays 93 5.3 Detection of biomolecules with SiNW FETs 102 5.3.1 General considerations for biodetection with FETs 102 5.3.2 Sensing aptamers with FETs 103 5.3.3 Biodetection of the analyte cortisol with SiNW FETs 104 5.3.4 Detection of cortisol with SiNW FETs 112 5.4 Summary 119 5.5 References 121 6 Summary and outlook 131 6.1 Summary 131 6.2 Perspectives – toward multiplexed biosensing applications 134 6.3 References 137 Appendix i A.1 Protocols i A.1.1 Functionalization of gold antennas with thiolated DNA i A.1.2 Functionalization of SiO2 with TESPSA and amino-modified receptors i A.1.3 Functionalization with APTES and carboxyl-modified receptors ii A.1.4 Preparation of microfluidic channels via soft lithography ii A.2 Predicted secondary structures iv A.2.1 Secondary structures of 100base pair target without probe-strands iv A.2.2 Secondary structures of 100base pair target with 25 base pair probe-strand x Versicherung xvii Acknowledgments xix List of publications xxi Peer-reviewed publications xxi Publications in preparation xxi Selected international conferences xxii Curriculum Vitae xxiiiBiosensors have proven to be indispensable in numerous vital areas. For example, detecting the presence and concentration of specific biomarkers requires sensitive and reliable measurement methods. Rapid developments in the field of nanotechnology lead to nanomaterials with new properties and associated innovative applications. Thus, nanotechnology has a far-reaching impact on biosensors' development, e.g., delivery of biosensing devices with greater sensitivity, shorter response times, and precise but cost-effective sensor platforms. In addition, nanobiosensors hold high potential for integration and miniaturization and can operate directly at the point of care - serving as a bridge between diagnostics and routine tests. This work focuses on applying nanostructured biosensors for the sensitive and label-free detection of analytes. A distinct aim is the continuous monitoring of biomarkers with compact read-out systems to provide direct, valuable feedback in real-time. The first step in achieving this goal is the adequate functionalization of nanostructured sensor surfaces with suitable receptors to detect analytes of interest. Due to their thermal and chemical stability with the possibility for customizable functionalization, DNA-based receptors are selected. Thereupon, universal strategies for confining nanobiosensor platforms are presented using different sensor systems, analytes, and characterization methods. As a first application, a plasmonic biosensor based on vertically aligned gold nanoantennas tracked the immobilization, blocking, and subsequent hybridization of DNA by means of localized surface plasmon resonance (LSPR). At the same time, the LSPR sensor was used to evaluate fundamental hybridization mechanisms on nanostructured and planar surfaces, emphasizing the unique optical properties of metallic nanostructures. In a second application, an electric sensor based on silicon nanowire field-effect transistors (SiNW FET) monitored the level of the stress marker cortisol in human saliva. Based on evaluating the underlying charge distributions within the resulting receptor-analyte complex of molecules, the detection of cortisol within the Debye length is facilitated. Thus, direct, label-free detection of cortisol in human saliva using SiNW FET was successfully applied to the developed platform and compared to cortisol levels obtained using a commercial alternative. In summary, both presented platforms indicate a highly versatile and beneficial performance of nanobiosensors for continuous detection of biomarkers in real-time and preferably point-of-care (POC).:Kurzfassung I Abstract III Abbreviations and symbols V Content VII 1 Introduction 1 1.1 Scope of the thesis 4 1.2 References 6 2 Fundamentals 9 2.1 Biosensors 9 2.2 Influence of nanotechnology on sensor development 10 2.3 Biorecognition elements 12 2.3.1 Biorecognition element: DNA 13 2.3.2 Aptamers 14 2.3.3 Immobilization of receptors 15 2.4 Transducer systems 17 2.4.1 Optical biosensors - surface plasmon resonance 17 2.4.2 Electric Biosensors – Field-effect transistors (FETs) 21 2.5 Metal oxide semiconductor field-effect transistor - MOSFET 21 2.6 Summary 26 2.7 References 27 3 Materials and methods 33 3.1 Plasmonic biosensors based on vertically aligned gold nanoantennas 33 3.1.1 Materials 33 3.1.2 Manufacturing of nanoantenna arrays 34 3.1.3 Surface modification and characterization 35 3.1.4 Measurement setup for detection of analytes 38 3.2 SiNW FET-based real-time monitoring of cortisol 40 3.2.1 Materials 40 3.2.2 Manufacturing of silicon nanowire field effect transistors (SiNW FETs) 42 3.2.3 Integration of SiNW FETs into a portable platform 42 3.2.4 Biomodification and characterization of electronic biosensors SiNW FETs 42 3.2.5 Electric characterization of FETs 47 3.3 References 50 4 Plasmonic DNA biosensor based on vertical arrays of gold nanoantennas 51 4.1 Introduction - Optical biosensors operating by means of LSPR 53 4.2 Biosensing with vertically aligned gold nanoantennas 56 4.2.1 Sensor fabrication, characterization, and integration 56 4.2.2 Integration of microfluidics 58 4.2.3 Immobilization of probe DNA and backfilling 58 4.2.4 Hybridization of complementary DNA strands 62 4.2.5 Surface coverage and hybridization efficiency of DNA 69 4.2.6 Refractive index sensing 72 4.2.7 Backfilling and blocking 73 4.3 Summary 75 4.4 References 77 5 Label-free detection of salivary cortisol with SiNW FETs 83 5.1 Introduction 85 5.2 Design, integration, and performance of SiNW FETs into a portable platform 89 5.2.1 Structure and electrical characteristics of honeycomb SiNW FETs 89 5.2.2 Integration of SiNW FET into a portable measuring unit 91 5.2.3 Performance of SiNW FET arrays 93 5.3 Detection of biomolecules with SiNW FETs 102 5.3.1 General considerations for biodetection with FETs 102 5.3.2 Sensing aptamers with FETs 103 5.3.3 Biodetection of the analyte cortisol with SiNW FETs 104 5.3.4 Detection of cortisol with SiNW FETs 112 5.4 Summary 119 5.5 References 121 6 Summary and outlook 131 6.1 Summary 131 6.2 Perspectives – toward multiplexed biosensing applications 134 6.3 References 137 Appendix i A.1 Protocols i A.1.1 Functionalization of gold antennas with thiolated DNA i A.1.2 Functionalization of SiO2 with TESPSA and amino-modified receptors i A.1.3 Functionalization with APTES and carboxyl-modified receptors ii A.1.4 Preparation of microfluidic channels via soft lithography ii A.2 Predicted secondary structures iv A.2.1 Secondary structures of 100base pair target without probe-strands iv A.2.2 Secondary structures of 100base pair target with 25 base pair probe-strand x Versicherung xvii Acknowledgments xix List of publications xxi Peer-reviewed publications xxi Publications in preparation xxi Selected international conferences xxii Curriculum Vitae xxii
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