Noble metal nanomaterials have numerous uses in plasmonic and surface enhanced Raman scattering (SERS) detection applications; however, upon the addition of analytes, nanomaterials often undergo uncontrolled aggregation which leads to inconsistent signal intensities. To overcome this limitation, the effect of gold nanosphere concentration, column purification, and surface chemistry functionalization using internally etched silica stabilization methods was investigated on SERS assays for small molecule detection. Nanostructure composition, size, shape, stability, surface chemistry, optical properties, and SERS-activity were monitored using localized surface plasmon resonance (LSPR or extinction) spectroscopy, transmission electron microscopy (TEM), and Raman spectroscopy. First, the behavior of citrate-stabilized gold nanospheres was monitored as a function of molecular surface coverage. Both extinction and SERS spectral intensities increased linearly below monolayer functionalization. Above this value, however, uncontrolled nanoparticle aggregation occurred and large but irreproducible SERS signal intensities were monitored. Next, gold nanoparticles were encapsulated with varying silica shell thicknesses and purified using traditional centrifugation steps and/or column chromatography. Relative to the traditionally purified (i.e. centrifuged) samples, the SERS responses from small molecules using the column purified nanoparticle samples followed a well-known SERS distance-dependence model. Thus, surface chemistry cannot form more than a 2 nm thick layer on gold nanospheres if SERS applications were targeted. To overcome these challenges, gold nanospheres encapsulated with a thick silica shell were made SERS-active by etching the internal silica layer near the metal surface. During the synthesis of these internally etched silica-coated gold nanospheres, the LSPR wavelength shift, a parameter related to the effective local refractive index near the gold core, was monitored instead of etching time, in order to produce nanostructures with more uniform internal silica etching from sample to sample. The SERS-activity of a target molecule using these nanostructures was measured as a function of LSPR wavelength shift. SERS signal intensity increased, which suggested that more analyte molecules were able to bind to the gold surface because of the larger pore size in the silica layer near the metal core. Further exploration of these findings should increase the integration of solution-phase nanoparticles in more predictable functions in future applications, resulting in more quantitative and reproducible molecular detection in complex sample matrices, including biological and environmental samples.

L' objet d'étude de cette thèse est l' origami d' ADN. Le nombre important d'applications utilisant cette technique, et leurs diversités, sont des preuves que ces structures présentées en 2007 sont une avancée importante pour la technologie ADN. Dans cette thèse nous présentons dans un premier temps les résultats de simulations sur les propriétés mécaniques de ces nouvelles structures. Les résultats d'expériences et de simulations sur le processus de formations pour de petites structures d'ADN et sur des origamis d'ADN sont présentés dans une deuxième partie. Finalement une application de ces structures à la détection SERS est proposée, et les résultats expérimentaux concernant la réalisation de cette structure sont discutés. / DNA origami are new nanostructures (2006) whose physical properties are still to be understood. In this work we were first interested in their mechanical properties. The first approach of this study was through the use of polymer physics, as it is the classical way to study DNA. We then used computer simulations to model the system in a more detailed manner and to extract general rules on the mechanical behaviour of DNA constructs. The other aspect that we studied is the process of formation of DNA origamis. We first realised an experimental study of the process of formation of the simplest origami that we could envision. This study was intended to investigate basic principles on the process of formation of DNA structures. A coarse grain model is then developed to have a first insight onto the formation process. Then an experimental study on large origamis follows with a modeling of the annealing and melting curves based on the principles determined from the study of the simplest origami. We also worked on the development of a SERS platform.

The accurate and rapid detection of clinically relevant analytes at the point-of-care (POC) is a crucial element for the increase in our quality of life. There are multiple detection techniques for sensing a target analyte in biological samples. However, electrochemical sensors excel because of their versatility, accuracy and sensitivity. Among the many challenges in the fabrication of electrochemistry-based POC sensors, the miniaturization of the working electrodes is one of the most difficult to overcome. Decreasing the size of the sensors will result in less electroactive surface area (ESA) and, therefore, lower sensitivity. Thus, the design of miniaturized electrodes with high ESA is desired in this research field. The methodology developed in our laboratory to accomplish this goal is based on the fabrication of microstructured gold electrodes (MSEs) by depositing, via sputtering, a gold thin-film onto a pre-stressed polystyrene substrate masked with adhesive vinyl stencils and thermally shrinking the substrate at high temperatures (135-160 °C). In my thesis work, I developed cost-effective sensitive electrochemical platforms using only bench-top approaches. First, the ESA and, thus, the sensitivity of the MSEs were enhanced by using a simple and rapid nano-roughening approach. The ESA of MSEs was increased 4x by applying high voltage pulsing in sulfuric acid. The resulting electrodes possessed high anti-fouling capabilities and excellent response toward the enzyme-free detection of glucose with a limit of detection (LOD) of 0.62 mM in the presence of bovine serum albumin (BSA) and ascorbic acid. Furthermore, the fabrication cost of the MSEs electrodes was decreased by 5x by replacing the sputtering deposition step with a cost-effective solution-based electroless deposition technique. In this case, the PS substrates were coated with a polydopamine adhesion layer and noble metal films (copper, silver and gold) were subsequently plated. Not only the cost of the gold electrode was substantially reduced but, due to the intrinsic roughness of the surface, the MSEs electrodes obtained via electroless deposition showed a higher ESA than those made via sputtering. Furthermore, the developed electroless method was extended for the fabrication of paper-based sensing devices. The sensing versatility of these surfaces was demonstrated by electrochemically detecting mercury with a 0.27 ppb LOD and by sensing thiophenol via surface-enhanced Raman scattering (SERS). The MSEs electrodes fabricated via electroless deposition were subjected to the nano-roughening technique to generate affordable and high ESA electrodes. These platforms were used to design enzyme-based biosensors to accurately detect glucose and urea in complex samples. Glucose was detected in four different types of wine, with matrix interference measured below 10%, and in human serum, with a measured concentration that was not statistically different from that obtained from commercially available biosensors. Urea was detected in human urine and plasma with matrix interferences measured to be below 8% in both cases. We envision that the fabrication techniques developed in this thesis will rapidly grow in the scientific community for the prompt and accurate design of POC electrochemical devices. / Thesis / Doctor of Philosophy (PhD)