Experiments were performed to study forced convective heat transfer of de-ionized water (DI water) and aqueous nanofluids flowing in a microchannel. An array of temperature nanosensors, called “Thin Film Thermocouples (TFT)”, was utilized for performing the experimental measurements. TFT arrays were designed (which included design of photomask layout), microfabricated, packaged and assembled for testing with the experimental apparatus. Heat removal rates from the heated surface to the different testing fluids were measured by varying the coolant flow rates, wall temperatures, nanoparticle material, nanoparticle morphology (shape and nanoparticle size) as well as mass concentrations of nanoparticles in the coolants. Anomalous thermal behavior was observed in the forced convective heat transfer experiments. Precipitation of the nanoparticles on the heat exchanging surface was monitored using Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray spectroscopy (EDX). Isolated precipitation of nanoparticles is expected to cause formation of “nanofins” leading to enhancement of surface area and thus resulting in enhanced convective heat transfer to the nanofluid coolants. However, excessive precipitation (caused due to the agglomeration of the nanoparticles in the nanofluid coolant) causes scaling (fouling) of the heat exchanging surfaces and thus results in degradation of convective heat transfer. This study shows that the surface morphology plays a crucial role in determining the efficacy of convective heat transfer involving suspensions of nanoparticles in coolants (or nanofluids). Flow visualization and quantitative estimation of near-wall temperature profiles were performed using quantum dots and fluorescent dyes. This non-contact measurement technique for temperature and flow profiles in microchannels using quantum dots is expected to make pioneering contribution to the field of experimental flow visualization and to the study of micro/nano-scale heat transfer phenomena, particularly for forced convective heat transfer of various coolants, including nanofluids. Logical extensions of this study were explored and future directions were proposed. Preliminary experiments to demonstrate feasibility showed significant enhancement in the flow boiling heat flux values for nanofluids compared to that of pure solvent (DIW). Based on the novel phenomena observed in this study several other topics for future research were suggested, such as, using Surface Plasmon Resonance (SPR) platforms to monitor precipitation of nanoparticles on microchannel surfaces in real time (e.g., for generating surface isotherms).

Philosophiae Doctor - PhD / Nowadays, the pollution of surface waters with chemical contaminants is one of the most crucial environmental problems. These chemical contaminants enter rivers and streams resulting in tremendous amount of destruction, so the detection and monitoring of these chemical contaminants results in an ever-increasing demand. This thesis describes the search for a suitable method for the determination of platinum group metals (PGMs) in environmental samples due to the toxicity of mercury films and the limitations with methods other than electroanalytical methods. This study focuses on the development of a novel bismuth-silver bimetallic nanosensor for the determination of PGMs in roadside dust and soil samples. Firstly, individual silver, bismuth and novel bismuth-silver bimetallic nanoparticles were chemically synthesised. The synthesised nanoparticles was compared and characterised by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), ultraviolet-visible spectroscopy (UV-Vis), Fourier-transformed infrared spectroscopy (FT-IR), Raman spectroscopy, and transmission electron microscopy (TEM) analysis to interrogate the electrochemical, optical, structural, and morphological properties of the nanomaterials. The individual silver, bismuth, and bismuth-silver bimetallic nanoparticles in the high resolution transmission electron microscopy results exhibited an average particle size of 10-30 nm. The electrochemical results obtained have shown that the bismuth-silver bimetallic nanoparticles exhibit good electro-catalytic activity that can be harnessed for sensor construction and related applications. The ultraviolet-visible spectroscopy, Fourier-transformed infrared spectroscopy, and Raman spectroscopy results confirmed the structural properties of the novel bismuth-silver bimetallic nanoparticles. In addition the transmission electron microscopy and selected area electron diffraction morphological characterisation confirmed the nanoscale nature of the bismuth-silver bimetallic nanoparticles. Secondly, a sensitive adsorptive stripping voltammetric procedure for palladium, platinum and rhodium determination was developed in the presence of dimethylglyoxime (DMG) as the chelating agent at a glassy carbon electrode coated with a bismuth-silver bimetallic nanofilm. The nanosensor further allowed the adsorptive stripping voltammetric detection of PGMs without oxygen removal in solution. In this study the factors that influence the stripping performance such as composition of supporting electrolyte, DMG concentration, deposition potential and time studies, and pH have been investigated and optimised. The bismuth-silver bimetallic nanosensor was used as the working electrode with 0.2 M acetate buffer (pH = 4.7) solution as the supporting electrolyte. The differential pulse adsorptive stripping peak current signal was linear from 0.2 to 1.0 ng/L range (60 s deposition), with limit of detections for Pd (0.19 ng/L), Pt (0.20 ng/L), Rh (0.22 ng/L), respectively. Good precision for the sensor application was also obtained with a reproducibility of 4.61% for Pd(II), 5.16% for Pt(II) and 5.27% for Rh(III), for three measurements. Investigations of the possible interferences from co-existing ions with PGMs were also done in this study. The results obtained for the study of interferences have shown that Ni(II) and Co(II) interfere with Pd(II), Pt(II) and Rh(III) at high concentrations. The interference studies of Cd(II), Pb(II), Cu(II) and Fe(III) showed that these metal ions only interfere with Pd(II) and Pt(II) at high concentrations, with no interferences observed for Rh(III). Phosphate and sulphate only interfere at high concentrations with Pt(II) and Rh(III) in the presence of DMG with 0.2 M acetate buffer (pH = 4.7) solution as the supporting electrolyte. Based on the experimental results, this bismuth-silver bimetallic nanosensor can be considered as an alternative to common mercury electrodes, carbon paste and bismuth film electrodes for electrochemical detection of PGMs in environmental samples. Thirdly, this study dealt with the development of a bismuth-silver bimetallic nanosensor for differential pulse adsorptive stripping voltammetry (DPAdSV) of PGMs in environmental samples. The nanosensor was fabricated by drop coating a thin bismuth-silver bimetallic film onto the active area of the SPCEs. Optimisation parameters such as pH, DMG concentration, deposition potential and deposition time, stability test and interferences were also studied. In 0.2 M acetate buffer (pH = 4.7) solution and DMG as the chelating agent, the reduction signal for PGMs ranged from 0.2 to 1.0 ng/L. The detection limit for Pd(II), Pt(II) and Rh(III) was found to be 0.07 ng/L, 0.06 ng/L and 0.2 ng/L, respectively. Good precision for the sensor application was also obtained with a reproducibility of 7.58% for Pd(II), 6.31% for Pt(II) and 5.37% for Rh(III), for three measurements. In the study of possible interferences, the results have shown that Ni(II), Co(II), Fe(III), Na+, SO42- and PO43- does not interfere with Pd(II) in the presence of DMG with sodium acetate buffer as the supporting electrolyte solution. These possible interference ions only interfere with Pt(II) and Rh(III) in the presence of DMG with 0.2 M acetate buffer (pH = 4.7) as the supporting electrolyte solution.

Safe drinking water is essential for life, yet at least two billion people around the world consume water contaminated with pathogens among other pollutants. Standard methods like polymerase chain reaction (PCR) and membrane filtration have been developed to detect enteric pathogens in water. However, these methods are limited in their accessibility due to long wait times to obtain results, and the requirements of skilled expertise, electricity, and laboratory equipment. This research has focused on addressing some of these limitations by analyzing the mechanisms of work and optimizing an indirect colorimetric nanosensor developed in previous research. The colorimetric nanosensor investigated herein relies on a competitive binding mechanism. When positively charged gold nanoparticles coated with polyethyleneimine (PEI-AuNPs) are added to a water sample containing negatively charged Escherichia coli (E. coli) and β-galactosidase (β-Gal) enzyme, the PEI-AuNPs will preferably bind to E. coli. This leaves β-Gal free in solution to hydrolyze chlorophenol red β-D-galactopyranoside (CPRG) (a substrate added to the water sample). The hydrolysis reaction of CPRG results in changing the solution color and the magnitude of this color change is a function of the amount of E. coli present in a water sample. It was hypothesized herein that the governing factor for the nanosensor functionality is the surface charge/Coulombic interactions rather than the nanoparticle composition or the type of chemical coating on the nanoparticle surface. To test the research hypotheses, positively charged nanoparticles with different compositions and chemical coatings as well as positively charged polymers were tested herein as potential detection agents for E. coli in water using the competitive binding assay reported in the literature with some modifications. This study produced three main findings that support the research hypotheses. First, gold nanoparticles (AuNPs) were not critical to the nanosensor functionality – other positively charged nanoparticles of silver and iron oxide coated with branched PEI were able to detect E. coli as low as 105 and 107 CFU/mL, respectively. Second, the branched PEI polymer itself (i.e., without a nanomaterial) detected E. coli at 107 CFU/mL. Third, in the absence of E. coli, (1-Hexadecyl) Trimethylammonium Bromide (CTAB), a positively charged polymer, inhibited the hydrolysis of CPRG by β-Gal. This inhibition suggests that other positively charged polymer types have potential applications in colorimetric detection assays that are based on the competitive binding mechanism. The observed behavior with the aforementioned sensing agents indicated that the positive charge was likely responsible for the detection of microbes using this competitive binding detection approach rather than the type of the chemical coating/agent used. These findings open possibilities for more types of recyclable and cost effective nanomaterials and polymers to be developed for detection of E. coli using this competitive binding approach. Furthermore, research is warranted for optimizing the sensing agents tested in this study to lower their detection limit and assess their recyclability.

Rapid and reliable diagnostics of a disease represents one of the main focuses of today’s academic and industrial research in the development of new sensor prototypes and improvement of existing technologies. With respect to demographic changes and inhomogeneous distribution of the clinical facilities worldwide, especially in rural regions, a new generation of miniaturized biosensors is highly demanded offering an easy deliverability, low costs and sample preparation and simple usage. This work focuses on the integration of nanosized electronic structures for high-specific sensing applications into adequate microfluidic structures for sample delivery and liquid manipulation. Based on the conjunction of these two technologies, two novel sensor platforms were prototyped, both allowing label-free and optics-less electrochemical detection ranging from molecular species to eukaryotic micron-sized human cells.:Table of Figures List of Tables Abbreviations List of Symbols 1 Introduction 1.1 Motivation 1.2 State of the art 1.3 Scope of this thesis 2 Fundamentals 2.1 Sensors at the nanoscale 2.2 Transistors technology 2.2.1 p-n junction 2.2.3 The MOSFET 2.2.4 The ISFET and BioFET 2.3 Impedance measurements for biodetection 2.3.1 Electrical impedance spectroscopy 2.3.2 Electrical impedance cytometry 2.4 Microfluidics 2.4.1 Definition 2.4.2 Droplet-based microfluidics 2.5 Biomarkers for sensing applications 2.5.1 Peripheral blood mononuclear cells (PBMCs) 2.5.2 Physical parameters 3. Material and methods 3.1 General 3.1.1 Materials and chemicals 3.1.2 Surface cleaning 3.2 Lithography 3.2.1 Electron beam lithography 3.2.2 Laser lithography 3.2.3 UV lithography 3.2.4 Soft lithography 3.3 Thermal deposition of metals 3.4 APTES functionalization 3.4.1 Fluorescent labeling of APTES 3.5 Measurement devices 3.5.1 SiNW FET measurements 3.5.2 Electrical Impedance cytometry measurements 3.6 Bacteria and cell cultivation 3.6.1 PBMC purification and treatment 3.6.2 Bacteria cultivation 4. Compact nanosensors probe microdroplets 4.1 Overview 4.2 Fabrication 4.2.1 SiNW FET fabrication 4.2.2 SiNW FET modification for top-gate sensing 4.3 Electrical characterization 4.4 Flow-focusing droplet generation 4.4.1 Flow-focusing geometry 4.4.2 Flow-focusing droplet characterization 4.4.3 Microfluidic integration 4.5 Deionized water droplet sensing 4.6 Phosphate-buffered saline (PBS) droplet sensing 4.6.1 Influence of the droplet’s ionic concentration 4.6.2 Plateau formation in dependence of the droplet’s settling time 4.6.3 Droplet analysis by their ratio 4.6.4 Dependence on pH value 4.6.5 Long time pH sensing experiment 4.6.6 Dependence on ionic concentration 4.7 Tracking of reaction kinetics in droplets 4.7.1 Principle and setup of the glucose oxidase (GOx) enzymatic test 4.7.2 GOx enzymatic assay 4.8 Stable baseline by conductive carrier phase 5. Impedance-based flow cytometer on a chip 5.1 Overview 5.2 Overview of the fabrication of the sensor device 5.3 COMSOL simulation of sensing area 5.3.1 Prototyping of the sensing geometry 5.3.2 Optimization of the sensing geometry 5.3.3 Evaluation of the working potential 5.3.4. Scaling of the sensing area 5.4 Fabrication of the nanoelectronic sensing structure 5.4.1 Nanofabrication and analysis 5.4.2 Evaluation of the proximity effect 5.5 Microcontacting of nanostructured sensing structures 5.6 Electrical characterization of the sensing structure 5.6.1 Characterization in alternating current 5.6.2 Characterization in direct current (DC) 5.7 Scaling effect of nanostructures in static sensing conditions 5.8 Multi-analyte detection on the sensor 5.9 Microfluidic focusing system 5.9.1 1D focusing using FITC-probed deionized water 5.9.2 2D Focusing using fluorescent microparticles 5.10 Microfluidic integration of the two technologies 5.11 Dynamic SiO2 particle detection 5.11.1 Single particle detection 5.11.2 Scatter plot representation 5.11.3 Effect of the sensing area in dynamic particle detection 5.11.4 Dynamic detection of SiO2 particles with different diameters 5.12 Detection of peripheral blood mononuclear cells (PBMCs) 5.12.1 Overview 5.12.2 PBMC classification detected by impedance cytometry 5.12.3 PBMC Long-time detection 5.13 Detection of acute myeloid leukemia by impedance cytometry 5.13.1 Manual analysis of the output response 5.13.2 Learning algorithm for automatic cell classification 5.14 Exploring the detection limit of the device 6. Summary and outlook Scientific output References Acknowledgements / Rasche und zuverlässige biologische Krankheitsdiagnostik repräsentiert eines der Hauptfokusse heutiger akademischer und industrieller Forschung in der Entwicklung neuer Sensor-Prototypen und Verbesserung existierender Technologien. In bezug auf weltweite demographische Änderungen und hohe Distanzen zu Kliniken, besonders in ländlichen Gegenden, werden zusätzliche Anfordungen an neue miniaturisierte Biosensor-Generationen gestellt, wie zum Beispiel ihre Transportfähigkeit, geringe Kosten und Probenpräparation, sowie einfache Handhabung. Diese Dissertation beschäftigt sich mit der Integration nanoskalierter Strukturen zur Detektion chemischer und biologischer Spezies und mikrofluidischen Kanälen zu deren Transport und zur Manipulation der Ströme. Basierend auf der Verbindung dieser beiden Technologien wurden zwei Sensor-Plattformen entwickelt, die eine markierungsfreie und nicht-optische elektrische Detektion von Molekülen bis zu eukaryotischen menschlichen Zellen erlauben.:Table of Figures List of Tables Abbreviations List of Symbols 1 Introduction 1.1 Motivation 1.2 State of the art 1.3 Scope of this thesis 2 Fundamentals 2.1 Sensors at the nanoscale 2.2 Transistors technology 2.2.1 p-n junction 2.2.3 The MOSFET 2.2.4 The ISFET and BioFET 2.3 Impedance measurements for biodetection 2.3.1 Electrical impedance spectroscopy 2.3.2 Electrical impedance cytometry 2.4 Microfluidics 2.4.1 Definition 2.4.2 Droplet-based microfluidics 2.5 Biomarkers for sensing applications 2.5.1 Peripheral blood mononuclear cells (PBMCs) 2.5.2 Physical parameters 3. Material and methods 3.1 General 3.1.1 Materials and chemicals 3.1.2 Surface cleaning 3.2 Lithography 3.2.1 Electron beam lithography 3.2.2 Laser lithography 3.2.3 UV lithography 3.2.4 Soft lithography 3.3 Thermal deposition of metals 3.4 APTES functionalization 3.4.1 Fluorescent labeling of APTES 3.5 Measurement devices 3.5.1 SiNW FET measurements 3.5.2 Electrical Impedance cytometry measurements 3.6 Bacteria and cell cultivation 3.6.1 PBMC purification and treatment 3.6.2 Bacteria cultivation 4. Compact nanosensors probe microdroplets 4.1 Overview 4.2 Fabrication 4.2.1 SiNW FET fabrication 4.2.2 SiNW FET modification for top-gate sensing 4.3 Electrical characterization 4.4 Flow-focusing droplet generation 4.4.1 Flow-focusing geometry 4.4.2 Flow-focusing droplet characterization 4.4.3 Microfluidic integration 4.5 Deionized water droplet sensing 4.6 Phosphate-buffered saline (PBS) droplet sensing 4.6.1 Influence of the droplet’s ionic concentration 4.6.2 Plateau formation in dependence of the droplet’s settling time 4.6.3 Droplet analysis by their ratio 4.6.4 Dependence on pH value 4.6.5 Long time pH sensing experiment 4.6.6 Dependence on ionic concentration 4.7 Tracking of reaction kinetics in droplets 4.7.1 Principle and setup of the glucose oxidase (GOx) enzymatic test 4.7.2 GOx enzymatic assay 4.8 Stable baseline by conductive carrier phase 5. Impedance-based flow cytometer on a chip 5.1 Overview 5.2 Overview of the fabrication of the sensor device 5.3 COMSOL simulation of sensing area 5.3.1 Prototyping of the sensing geometry 5.3.2 Optimization of the sensing geometry 5.3.3 Evaluation of the working potential 5.3.4. Scaling of the sensing area 5.4 Fabrication of the nanoelectronic sensing structure 5.4.1 Nanofabrication and analysis 5.4.2 Evaluation of the proximity effect 5.5 Microcontacting of nanostructured sensing structures 5.6 Electrical characterization of the sensing structure 5.6.1 Characterization in alternating current 5.6.2 Characterization in direct current (DC) 5.7 Scaling effect of nanostructures in static sensing conditions 5.8 Multi-analyte detection on the sensor 5.9 Microfluidic focusing system 5.9.1 1D focusing using FITC-probed deionized water 5.9.2 2D Focusing using fluorescent microparticles 5.10 Microfluidic integration of the two technologies 5.11 Dynamic SiO2 particle detection 5.11.1 Single particle detection 5.11.2 Scatter plot representation 5.11.3 Effect of the sensing area in dynamic particle detection 5.11.4 Dynamic detection of SiO2 particles with different diameters 5.12 Detection of peripheral blood mononuclear cells (PBMCs) 5.12.1 Overview 5.12.2 PBMC classification detected by impedance cytometry 5.12.3 PBMC Long-time detection 5.13 Detection of acute myeloid leukemia by impedance cytometry 5.13.1 Manual analysis of the output response 5.13.2 Learning algorithm for automatic cell classification 5.14 Exploring the detection limit of the device 6. Summary and outlook Scientific output References Acknowledgements

Optische Sonden für die Bildgebung auf Grundlage des pH-Wertes sind für die Wissenschaft von großem Interesse, da es sich beim pH-Wert um eine entscheidende Kenngröße für viele Prozesse in der Biotechnologie, Biologie, medizinische Diagnostik, biomedizinische Forschung und Materialkorrosion handelt. Optische pH-Sensoren, deren Funktionsprinzip auf dem photophysikalischen Prozess Fluoreszenz basieren, sind dabei von besonderem Interesse, da die Fluoreszenz eine sehr hohe Empfindlichkeit, welche sogar die Auflösung einzelner Moleküle ermöglicht, bietet. Dies ermöglicht den Einsatz von molekularen über nanoskaligen Sensorformaten bis hin zur Anwendung in planaren Optoden oder faseroptischen Sensoren, und gilt, neben der nicht-invasiven, zerstörungsfreien und kontaktlosen Natur optischer Fluoreszenzmessungen, als anwendungsfreundliche Eigenschaft dieser optischen Sensoren. Der Informationsgehalt fluoreszenzintensität-basierender Sensoren ist normalerweise unspezifisch auf die An- oder Abwesenheit des Fluorophors und des Analyten beschränkt. Weiterhin kann er durch Schwankungen der Intensität des Anregungslichts und Änderungen der Fluorophorkonzentration, z.B. durch Photodegradation, beeinflusst werden. Daher werden Fluoreszenzsensoren oftmals in referenzierten Systemen verwendet. Diese Systeme ermöglichen, durch die Einführung einer analyt-inerten Referenz, ein duales, ratiometrisches Auslesen der Fluoreszenzintensitäten von zwei spektral unterscheidbaren Komponenten. In dieser Arbeit wird das konzeptionelle Design einer modular variierbaren, auf mehreren Komponenten basierenden Plattform für die ratiometrische optische Analytmessung vorgestellt. Dazu wurden fluoreszente, leicht zugängliche und analyt-sensitive Boron-Dipyrromethene (BODIPYs) mit durch nahes Infrarot (NIR) anregbare, mehrfarbig emittierende Aufkonvertierungs-Nanopartikel (UCNPs) kombiniert. Das Sensorprizip beruht dabei auf einem inneren Filter-Effekt der spektral abgestimmten Komponenten. / Optical probes for monitoring, imaging, and sensing of pH are of great interest for the scientific community as pH is a crucial marker for many processes in biotechnology, biology, medical diagnostics, biomedical research, and material corrosion. Thereby, optical pH sensors based on fluorescence have attracted interest in particular as fluorescence offers a high sensitivity down to the single molecule level, can be read out with relatively simple and readily miniaturized instrumentation, and allows online in situ measurements. Also the versatility ranging from molecular and nanosensor formats to planar optodes and fiber-optic sensors, and the non-invasive, non-destructive, and contactless nature of the measurement are application-friendly features. The information content, which is offered by a fluorescence intensity-based sensor, is usually unspecific and limited on the presence or the absence of the chromophore or analyte and can additionally be hampered by fluctuation of the excitation light intensity and changes in fluorophore concentration, e.g., due to photobleaching. Therefore, many fluorescence sensors are utilized in referenced systems, which enable twowavelength ratiometric measurements of the fluorescence intensity by the introduction of an analyte-inert reference with a spectrally distinguishable emission. This work presents the rational design of a versatile, modular, multi-component-based platform for ratiometric optical analyte sensing that can be simply adapted to different formats and measurement geometries. Therefore, readily available analyte-responsive fluorescent boron-dipyrromethene (BODIPY) dyes and near infrared (NIR)-excitable multicolouremissive upconversion nanoparticles (UCNPs) were combined utilizing an inner filter-based strategy with spectrally matched moieties.

Lumineszenzmessungen und Lumineszenz-Bildgebung spielen in den Biowissenschaften eine wichtige Rolle und ermöglichen den Nachweis und die Detektion von biomolekularen Wechselwirkungen und Analyten, die selbst keine intrinsische Farbe und / oder Lumineszenz aufweisen. Ein vielversprechender Ansatz ist die Verwendung von im Nahinfrarot (NIR) anregbaren, mehrfarbig emittierenden Aufkonversions-Nanokristallen (UCNPs) wie mit Yb3+ und Er3+ dotierten NaYF4-Nanopartikeln. Diese Nanopartikel können als Lumineszenzreporter oder Energiedonoren (Nanolampen) für die Anregung von Analyt-sensitiven Sonden benutzt werden. In dieser Arbeit, die den Aufbau eines selbstreferenzierten UCNP-basierten Sensors für die Ermittlung von pH-Werten als Ziel hatte, wurden beide Sensorkomponenten gezielt ausgewählt, synthetisiert und spektroskopisch charakterisiert. Dies beinhaltete i) UCNPs mit unterschiedlichen Größen, Partikelarchitekturen und Oberflächenfunktionalisierungen oder -beschichtungen und ii) Rosamin-Farbstoffe mit Absorptions- und Emissionseigenschaften, die für die gewünschte Kombination mit UCNPs geeignet sind. Des Weiteren wurde eine umfassende Untersuchung der chemischen Stabilität von unterschiedlich oberflächenfunktionalisierten und beschichteten UCNPs in biologisch relevanten Puffern durchgeführt. Für die schnelle Ermittlung der UCNP-Stabilität wurde eine einfache optische Überwachungsmethode zum Nachweis der Partikeldisintegationentwickelt, die die Abhängigkeit der UC-Lumineszenz und ihrer Lebensdauer von der Partikelgröße und Oberfläche ausnutzt. Im letzten Teil der Doktorarbeit wurden pH-Sensorfilme und Nanosensoren durch die Kombination der optimierten Yb3+, Er3+-co-dotierten UCNPs mit den pH-sensitiven Rosaminfarbstoffen als Energie-Akzeptoren unter Verwendung eines einfachen inneren Filters (Reabsorption) oder eines RET – Sensorkonzept konstruiert. / Luminescence sensing and imaging play an important role in the life sciences, enabling the detection and monitoring of biomolecular interactions and molecular targets that have no intrinsic colour and/or luminescence even in complex biological samples. A very promising approach presents the utilization of near-infrared (NIR) excitable multi-colour emissive upconversion nanocrystals (UCNPs) like NaYF4 nanoparticles doped with Yb3+ and Er3+ as luminescent reporters and as energy donors or “nanolamps” for the excitation of analyte-responsive probes. In this work, aiming at the design of self-referenced UCNP-based sensors for pH, both sensor components were rationally designed, synthesized, and spectroscopically characterized. This included i) UCNPs with different sizes, architectures, and surface chemistries or coatings and ii) rosamine dyes with absorption and emission properties adapted to the UC emission of the NaYF4: Yb3+, Er3+-doped UCNPs. Additionally, an extensive study of the chemical stability of differently surface functionalized and coated UCNPs in biologically relevant buffers was performed. To simplify stability monitoring, an optical monitoring method was developed for the detection of particle disintegration utilizing the size and environment dependence of the UC emission intensity and decay kinetics. Finally, pH sensor films and nanosensors were constructed by combining the initially optimized Yb3+, Er3+ co-doped UCNPs with pH-responsive rosamine dyes acting as energy acceptors utilizing a simple inner filter (reabsorption)- and a RET-based sensor concept.

Phospholipid vesicles are biocompatible, and have potential for intracellular applications, but minimal membrane integrity limits their use in membrane-rich environments. Stabilized membranes overcome this limitation while maintaining biocompatible surface structures. Additionally, the modularity of phospholipid bilayer makes them ideal components when designing biologically inspired sensors. Membrane composition can be tailored to specific applications, transmembrane proteins can provide added functionalities, and the isolated interior can prevent cytotoxic and interfering detection chemistries from altering the cellular environment. This work has focused on expanding the capabilities of stabilized phospholipid membranes, and determining which formulations hold promise in developing stabilized phospholipid vesicle nanosensors.Current membrane stabilization methods suffer from either incomplete stabilization, or irreversible stabilization limiting the applications of vesicle nanosensors. Therefore, a facile method to prepare robust phospholipid vesicles using commonly available phospholipids stabilized via the formation of an interpenetrating, acid-labile, cross-linked polymer network that imparts controlled polymer destabilization and subsequent vesicle degradation was developed. Upon exposure to acidic conditions, the highly cross-linked polymer network was converted to linear polymers, substantially reducing vesicle stability upon exposure to chemical and physical insults. The resultant transiently stabilized vesicles have potential for enhanced drug delivery and chemical sensing applications requiring minimal membrane defects, and allow for improved physiological clearance.Some vesicle nanosensor schemes may require the passive diffusion of low molecular weight species across the membrane in addition to controllable degradation. Therefore, the acid-degradable, polymer-stabilized, phospholipid vesicle production method was extended to bis-SorbPC membranes by simultaneously polymerizing the vesicle with an acetal-containing cross-linker. The vesicles display prolonged stability under physiological conditions, and significant additional stability compared to vesicles composed of naturally occurring phospholipids. The vesicles demonstrated potential utility for sensing and therapeutic applications.Phospholipid vesicles can also serve as labels to observe movement in macromolecular biological assemblies, but a dearth of caged fluorescent labels limits design and function. Therefore, the first caged fluorescent thiol was synthesized, shown to label amines rapidly, and demonstrated the required photolytic properties. The caged fluorescent thiol has potential as a label in observing the movement of macromolecular biological assemblies and as a fluorescent probe for observing endosomal trafficking and release.

La pollution des eaux par des composés organiques constitue un problème mondial majeur. Parmi cescomposés, les molécules aromatiques de faibles masses molaires constituent une famille largementrependue dont la toxicité et la cancérogénicité est avérée et bien documentée. La Directive-CadreEuropéenne sur l’eau (2000/60/EC, 2006/118/EC and 2006/11/EC) établit des normes de qualitéenvironnementales ayant pour objectif d’améliorer la qualité des eaux. Dans ce contexte, ledéveloppement d’outils analytiques robustes, permettant de détecter et de quantifier précisément et insitula présence de polluants dans les eaux est d’une importante primordiale. L’objectif principal de cetteétude est l’élaboration de nanocapteurs sensibles, robustes et réutilisables, permettant l’analyse depolluants organiques dans les eaux grâce à la Spectroscopie Raman Exaltée de Surface (SERS).Tout d’abord, une attention particulière a été portée à la sélection des récepteurs et des différentesstratégies de fonctionnalisation permettant d’élaborer un nanocapteur SERS capable de pré-concentrerles polluants visés. L’utilisation d’antigènes et de fragments d’antigènes (F(ab)2) a montré des résultatsprometteurs pour l’élaboration de nanocapteurs très sélectifs. Une seconde approche basée surl’utilisation de cavitants ou molécules hôtes, telles que les cyclodextrines (CDs), a été développée. Lapré-concentration sélective des polluants grâce à leur taille a été démontrée par spectroscopie Raman etSERS. Enfin, grâce à la possibilité d’identification moléculaire en milieu complexe offerte par laspectroscopie SERS, une approche permettant une pré-concentration non spécifique des polluants a étédéveloppée. Pour ce faire, différents sels de diazoniums (DSs) ont été synthétisés et greffés à la surfacedes nanocapteurs afin de créer une couche hydrophobe permettant la pré-concentration et la détection decomposés apolaires. Les performances de ces nano-capteurs ont été démontrées pour la détection de plusieurs PAHs apolaires. / Environmental water pollution by organic compounds is in continues worldwide concern. Low molecular mass aromatic molecules consisting in benzene rings have received considerable attention due to a documented significant toxicity and carcinogenicity. Within the objectives of the European Water Framework Directives (2000/60/EC, 2006/118/EC and 2006/11/EC) aiming in water quality improvement, the development of analytical tools allowing in-situ accurate and sensitive detection is of primary importance and would be a meaningful innovation. With this regard, the main scope of this study was to design sensitive, reproducible, specific and reusable nanosensor for the detection of organic pollutants in environmental waters using Surface Enhanced Raman Spectroscopy (SERS).During this study the main attention was paid to the selection of suitable receptors and strategies for SERS nanosensor surface functionalisation in order to preconcentrate targeted pollutants. The application of antibodies and antigen binding fragments (F(ab)2) for surface decoration was found to be promising approach for highly selective nanosensor design. Another strategy exploited during this study was related with an application of cyclodextrins (CDs). Using Raman and SERS spectroscopies the size selective encapsulation of analytes was demonstrated. Finally, taking advantage of molecular identification in the complex environments offered by SERS technique, nanosensors providing non-specific molecular pre-concentration was considered. For this purpose several diazonium salts (DSs) were studied and applied to the surface functionalisation to create highly hydrophobic coating layer. The performance of such nanosensor was evaluated by detection of aromatic pollutants.

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Les transistors à effet de champ sensibles aux ions (ISFET) sont des composants électroniques conçus pour fonctionner en phase liquide. Pour résumer, ce sont des MOSFET dont la grille métallique est remplacée par une membrane isolante ionosensible. Au début des années 2000, ces composants ont évolué avec l'introduction des premiers dispositifs à base de nanofils de silicium. Grâce à leurs faibles dimensions, ces capteurs ont ouvert de nouvelles perspectives, comme par exemple, l'étude des métabolismes intracellulaires. L'objectif de cette thèse a été de développer et d'étudier un capteur de type ISFET, à base de nanofils de silicium, ayant comme couche sensible l'alumine Al2O3. Les premiers travaux ont porté sur l'intégration de films minces d'alumine Al2O3 dans un procédé de type MOSFET. Ce matériau devant être déposé sur des nanofils de silicium, la technique de dépôt successif de couches moléculaires (Atomic Layer Deposition ALD) a été retenue. Cette méthode offre la possibilité de déposer des films d'épaisseur homogène tout autour des nanofils. Après l'étude de l'ALD-Al2O3, la deuxième grande partie de ce projet a consisté à développer, en utilisant les techniques de la microélectronique, des structures innovantes à base de nanofils de silicium. Des transistors constitués d'un seul nanofil, et d'autres constitués de réseaux parallèles de nanofils ont été réalisés. Ces capteurs ont été intégrés dans des canaux microfluidiques, permettant ainsi de localiser précisément le liquide sur les nanofils, mais aussi de pouvoir travailler en micro/nanovolumes. La dernière partie de ce projet a consisté à caractériser ces capteurs en phase liquide. Les différentes configurations ont montré leurs avantages et inconvénients en termes de transconductance, courants de fuite, pentes sous le seuil, sensibilités au pH et aux ions interférents (Na+ et K+). Les caractérisations se sont avérées excellentes et laissent entrevoir des perspectives intéressantes pour des applications biologiques. Les principales innovations de ces capteurs concernent : l'utilisation de nanofils suspendus, la réalisation d'une gaine isolante ionosensible bicouche SiO2/Al2O3 tout autour des nanofils, la variation du dopage le long des nanofils ce qui a conduit à la réalisation de jonctions N+/P/N+, et l'intégration des capteurs dans des canaux microfluidiques couverts. / Ion-sensitive field effect transistors (ISFET) are electronic components designed to operate in liquid phase. To summarize, they are MOSFET-based devices whose metal gate is replaced by an ionosensitive insulating layer. In the early 2000s, these components evolved with the introduction of the first device based on silicon nanowires. Thanks to their small dimensions, these sensors opened up new perspectives, such as the study of intracellular metabolisms. The aim of this thesis was to develop and study a type of ISFET sensor, based on silicon nanowires, with Al2O3 alumina as sensitive layer. The first part of this work was focused on the integration of thin alumina Al2O3 films in a MOSFET process. This material had to be deposited on silicon nanowires, that is why Atomic Layer Deposition (ALD) was used. This method allows to deposit films with uniform thickness all around nanowires. After the study of ALD-Al2O3, the second major part of this project was to develop innovative structures, based on silicon nanowires, using microelectronics methods. Transistors consisting of a single nanowire, and others consisting of parallel networks of nanowires were fabricated. These sensors were integrated in microfluidic channels, allowing to precisely locate the liquid on nanowires and also to work in micro/nanovolumes. The last part of this project consisted in characterizing these sensors in liquid phase. The different configurations showed their advantages and disadvantages in terms of transconductance, leakage currents, slopes below the threshold, sensitivities to pH and interfering ions (Na+ and K+). The characterizations proved to be excellent and suggest interesting prospects for biological applications. The main innovations of these sensors are: the use of suspended nanowires, the realisation of a bilayer SiO2/Al2O3 ion-sensitive sheath all around the nanowires, the doping variation along the nanowires which led to the realization of N+/P/N+ junctions, and the integration of sensors into covered microfluidic channels.