Biosensors and Nanobiosensors: Design and Applications

The goal of this chapter is to cover the full scope of biosensors. It offers a survey of the principles, design, operation, and biomedical applications of the most popular types of biosensing devices in use today. By discussing recent research and future trends based on many excellent books and reviews, it is hoped to give the readers a comprehensive view on this fast growing field

A high aspect ratio Fin-Ion Sensitive Field Effect Transistor: compromises towards better electrochemical bio-sensing

The development of next generation medicines demand more sensitive and reliable label free sensing able to cope with increasing needs of multiplexing and shorter times to results. Field effect transistor-based biosensors emerge as one of the main possible technologies to cover the existing gap. The general trend for the sensors has been miniaturisation with the expectation of improving sensitivity and response time, but presenting issues with reproducibility and noise level. Here we propose a Fin-Field Effect Transistor (FinFET) with a high heigth to width aspect ratio for electrochemical biosensing solving the issue of nanosensors in terms of reproducibility and noise, while keeping the fast response time. We fabricated different devices and characterised their performance with their response to the pH changes that fitted to a Nernst-Poisson model. The experimental data were compared with simulations of devices with different aspect ratio, stablishing an advantage in total signal and linearity for the FinFETs with higher aspect ratio. In addition, these FinFETs promise the optimisation of reliability and efficiency in terms of limits of detection, for which the interplay of the size and geometry of the sensor with the diffusion of the analytes plays a pivotal role.Comment: Article submitted to Nano Letter

Silicon on Isolator Ribbon Field-Effect Nanotransistors for High-Sensitivity Low-Power Biosensors

Silicon field-effect transistors (FETs) are an established technology for sensing applications. Recent advancements and the use of high-performance multigate FETs in computing technology raise new opportunities and questions about the most suitable device sensing architecture. In this work, we propose pH sensors exploiting ribbon (tri-date) FETs fabricated on investigated silicon nanowires and silicon-on-insulator substrates by a fully CMOS compatible approach. The FET characteristics were optimized using 3D modeling performed by the TCAD computer-aided design software package, depending on the topological parameters of the transistor and the level of control voltage. N-channel fully depleted ribbon FETs with critical dimensions in the order of 30 nm and SiO2 as a subgate insulator were developed and characterized. It was established that thin structures with a width of slightly than more 100 nm, a thickness of 40 nm, and a reduced doping level have high sensitivity and low energy consumption. They showed excellent electrical properties, subthreshold swing (SS) was about 90 mV/dec, and the on-to-off current ratio, Ion/Ioff, was about 105. The same architecture was tested as a highly sensitive, stable and reproducible pH sensor. The average internal sensitivity, S, was equal 34 mV/pH or 360 nA/pH. Sensitivity to pH, estimated in terms of relative changes in the threshold voltage, was 74%, and the maximum drain current was 40%. The maximum drain current of 85 μA at V ds = 1.0 V suggests successful low-power operation of the proposed device

Silicon on Isolator Ribbon Field-Effect Nanotransistors for High-Sensitivity Low-Power Biosensors

Silicon field-effect transistors (FETs) are an established technology for sensing applications. Recent advancements and the use of high-performance multigate FETs in computing technology raise new opportunities and questions about the most suitable device sensing architecture. In this work, we propose pH sensors exploiting ribbon (tri-date) FETs fabricated on investigated silicon nanowires and silicon-on-insulator substrates by a fully CMOS compatible approach. The FET characteristics were optimized using 3D modeling performed by the TCAD computer-aided design software package, depending on the topological parameters of the transistor and the level of control voltage. N-channel fully depleted ribbon FETs with critical dimensions in the order of 30 nm and SiO2 as a subgate insulator were developed and characterized. It was established that thin structures with a width of slightly than more 100 nm, a thickness of 40 nm, and a reduced doping level have high sensitivity and low energy consumption. They showed excellent electrical properties, subthreshold swing (SS) was about 90 mV/dec, and the on-to-off current ratio, Ion/Ioff, was about 105. The same architecture was tested as a highly sensitive, stable and reproducible pH sensor. The average internal sensitivity, S, was equal 34 mV/pH or 360 nA/pH. Sensitivity to pH, estimated in terms of relative changes in the threshold voltage, was 74%, and the maximum drain current was 40%. The maximum drain current of 85 μA at V ds = 1.0 V suggests successful low-power operation of the proposed device

Recent trends in field-effect transistors-based immunosensors

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Immunosensors are analytical platforms that detect specific antigen-antibody interactions and play an important role in a wide range of applications in biomedical clinical diagnosis, food safety, and monitoring contaminants in the environment. Field-effect transistors (FET) immunosensors have been developed as promising alternatives to conventional immunoassays, which require complicated processes and long-time data acquisition. The electrical signal of FET-based immunosensors is generated as a result of the antigen-antibody conjugation. FET biosensors present real-time and rapid response, require small sample volume, and exhibit higher sensitivity and selectivity. This review brings an overview on the recent literature of FET-based immunosensors, highlighting a diversity of nanomaterials modified with specific receptors as immunosensing platforms for the ultrasensitive detection of various biomolecules.Immunosensors are analytical platforms that detect specific antigen-antibody interactions and play an important role in a wide range of applications in biomedical clinical diagnosis, food safety, and monitoring contaminants in the environment. Field-effec44FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)2013/22127-2; 2016/04739-9sem informação: The authors acknowledge the financial assistance provided by The São Paulo Research Foundation (FAPESP, project #2013/22127-2 and grant #2016/04739-9) and the National Council for Scientific and Technological Development (CNPq

General Approach to Model the Surface Charge Induced by Multiple Surface Chemical Reactions in Potentiometric FET Sensors

We propose a general methodology to calculate the individual sensitivity and the cross-sensitivities of potentiometric sensor devices (e.g., ion sensitive FETs (ISFETs), CHEMFETs) with an arbitrary number of non-interacting receptors binding to ionic species or analytes in the electrolyte. The surface charge generated at the (bare or functionalized) interface with the electrolyte is described by the Poisson equation coupled to a linear system of equations for each type of receptor, where the unknowns are the fractions of sites binding with a given ion/analyte. Our general model encompasses in a unique framework a few simple special cases so far separately reported in the literature and provides for them closed-form expressions of the average site occupation probability. Detailed procedural description of the usage and benefits of the model is shown for specific cases with concurring surface chemical reactions

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

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

Field-Effect Sensors

This Special Issue focuses on fundamental and applied research on different types of field-effect chemical sensors and biosensors. The topics include device concepts for field-effect sensors, their modeling, and theory as well as fabrication strategies. Field-effect sensors for biomedical analysis, food control, environmental monitoring, and the recording of neuronal and cell-based signals are discussed, among other factors