This thesis presents experimental work with the primary aim of developing new approaches for the detection and characterisation of nanoparticles via electrochemical methods. The first chapter introduces the fundamental aspects of electrochemistry while the second chapter discusses the need for nanoparticle detection methods and the nonelectrochemical and electrochemical techniques that are currently used in the measurement of nanoparticles. A novel way to quantify silver nanoparticles in aqueous solution is proposed via nanoparticle-electrode impact experiments. In this technique a suitably potentiostatted electrode is immersed in a nanoparticle solution so as to bring about the oxidation or reduction of a single nanoparticle upon its collision with the electrode surface. This “direct” nanoparticle impact technique is then employed to detect laboratory synthesised silver nanoparticles in seawater. It is further shown that this method is capable of sizing silver nanoparticles contained in a commercially available cleaning product. Commercial silver nanoparticles are subsequently monitored via a sticking and stripping technique where homemade gold electrodes fabricated from CDs are immersed in a seawater sample spiked with nanoparticles prior to stripping voltammetry. The reduction of hydrogen peroxide on the surface of silver nanoparticles impacting upon an electrode is also examined. This “indirect” nanoparticle detection method is shown to provide an accurate route to nanoparticle sizing. A Fickian model is subsequently proposed to describe nanoparticle transport to the substrate electrode in both direct and indirect nanoparticle detection techniques. The importance of determining the proportion of nanoparticles which adhere to the electrode surface upon impact is highlighted and the sticking coefficient of a gold nanoparticle at a carbon surface determined. This technique to monitor nanoparticle sticking is optimised by chemical modification of the substrate electrode in order to achieve a “sticky” surface improving the rate of silver nanoparticle sticking. Finally, the nanoparticle collision method is shown to be applicable to C₆₀ nanoparticles where their detection and sizing is achieved in non-aqueous conditions. The methods developed in this thesis make a significant contribution to the promising application of electrochemical techniques in the detection and characterisation of single nanoparticles.

Dans cette thèse, des réseaux de nano- et micro-capteurs électrochimiques et opto-électrochimiques sont fabriqués en utilisant la technique de microfabrication « template synthesis ». Dans une première partie, des ensembles de nanoélectrodes (NEEs) sont utilisés comme plate-forme pour obtenir un biocapteur. Les NEEs sont préparés par déposition d’or dans une membrane poreuse en polycarbonate. L’originalité de notre approche a été de modifier la membrane de polycarbonate entourant les NEEs et non les NEEs elles-mêmes. La peroxydase de raifort (HRP) qui est fixée sur un anticorps secondaire a servi comme marqueur. Cette enzyme catalyse la réduction de H2O2 qui est ajouté en solution. En utilisant un système de détection dérivé de l'approche ELISA (Enzyme- Linked Immuno-Sorbants Assay), le récepteur de la protéine HER2 a été pris comme analyte cible. Il s’agit d’une protéine très importante puisqu’elle permet de dépister le cancer du sein. Dans une seconde partie, un réseau ordonné de sondes opto-électrochimiques est développé sur la face distale d’un faisceau de fibres optiques qui a été attaquée sélectivement par voie humide. Une structure macroporeuse est fabriquée en utilisant un cristal colloïdal comme « template ». L’or est ensuite déposé dans les interstices avant de dissoudre les nanoparticules de latex formant le cristal colloïdal. Ce réseau de microcavités macroporeuses a été testé avec succès comme substrat pour des mesures de Raman exalté de surface (SERS). / In this thesis, arrays of nano- and microelectrodes are developed to obtain electrochemical and optoelectrochemical sensors, by using the template synthesis as a microfabrication technique. In the first part, ensembles of nanoelectrodes (NEEs), obtained using a track-etched polycarbonate membrane as template, are functionalised in order to obtain electrochemical immunosensors. A biorecognition chain, antigen-antibody, is immobilized on the wide polycarbonate membrane letting uncovered the gold nanodisk electrodes. A label redox enzyme, linked to the biorecognition chain, is recognized and quantified electrochemically. Two different detection schemes are developed and low protein detection limits are achieved. In the second part, a macroporous micrometer sized opto-electrochemical sensor is developed on the distal face of an imaging fiber (coherent optical fiber bundle). A microwell array is obtained by controlled chemical etching, by exploiting the different chemical composition between cores and clads. Colloidal templates are created inside the microcavities, using polystirene beads of 280 nm. Gold is deposited inside the cavities, filling the void in the colloidal template, exploiting electroless and electrochemical deposition techniques. The gold macroporous structure inside the wells is successfully tested as SERS substrate.

Dans ce travail, plusieurs méthodes opto-électrochimiques ont été développées et appliquées à l’étude de systèmes chimiques à l’échelle de l’objet individuel. Du coté optique,l’holographie et la spectroscopie visible ont été associées à la super localisation pour pousser l’applicabilité de ces techniques au-delà de la limité imposée par la diffraction.Des techniques nanoélectrochimiques, comme les impacts stochastiques et l’utilisation de nanoelectrodes, complètent cette étude en renseignant sur la réactivité et sur les étapes de transfert d’électrons. Ces études couplées caractérisent ainsi les phénomènes chimiques de façon bien plus complète. Il est montré que cette caractérisation à la fois chimique et optique est en fait essentielle pour pouvoir comprendre le fonctionnement des systèmes nano chimiques in loco.En démarrant par des réactions modèle, comme l’oxydation de l’argent, la complexité des systèmes étudiés est progressivement augmentée, éclairant des phénomènes de transport,d’agrégation, ainsi que des transformation redox et de catalyse sur des matériaux complexes et mal définis tel que les oxydes de métaux de transition (cobalt) / A number of coupled optical and electrochemical single particle techniques are employed for investigating a variety of chemical systems at the level of individual objects.On the optical side, holography and visible spectroscopy are imbued with superlocalization principles pushing the applicability of these techniques down to sub-diffraction levels. Nanoelectrochemical techniques such as stochastic impacts and nanoelectrodes are used to complement this information, providing a much more complete characterization of the phenomena.It is shown that this dual optical and electrochemical single particle characterizationis actually crucial to understand complex nano chemical systems in loco. Starting frommodel reactions, such as Ag oxidation, the complexity of the studied phenomena and systems is progressively increased, as light is shed on transport phenomena, aggregation,as well as redox transformations and catalysis on complicated materials such as ill-defined transition metal (cobalt) oxides

In this work, we use optical methods to study electrochemical reactions and processes occurring on the nanometer length scale. Optical methods are advantageous over traditional electrochemical methods because of their high spatial resolution and sensitivity at both the single nanoparticle and single molecule level. This dissertation describes a series of studies in which super-localization and dark-field optical imaging is used to provide insight into spatial and temporal heterogeneity in nanoscale electrochemical systems with <25 nm spatial resolution. In the first set of experiments, three-dimensional (3-D) super-resolution imaging is used to determine the tip-substrate distance in nanoscale scanning electrochemical microscopy (SECM) with precision better than 25 nm. Correlating the tip-substrate distance using both optical and electrochemical techniques showed excellent agreement. Second, single nanoparticles (NP) were delivered through a nanopipette, and their resistive-pulse signals were correlated with a fluorescence optical signal. The diffusion trajectories of individual NP delivered to the external solution and to an electrified interface were obtained by 3-D super-resolution imaging, and showed signatures of both sub-diffusive and super-diffusive behavior, depending on the balance of forces between the flow from the pipette and the applied potential at the electrified substrate. Next, we studied the influence of surface oxide layers on single silver NP electrodissolution by tracking the intensity and spatial variation of scattering from single nanoparticles over time. We discovered that silver NPs can undergo electrodissolution in either a spatially symmetric or asymmetric manner, based on the nature of the surface oxide layer. Moreover, we also reported the simultaneous electrodeposition of silver oxide at the electrode surface during the electrodissolution of silver NPs, which enabled us to study the effect of multiple simultaneous redox reactions and their effects on one another. Overall, these experiments reveal local heterogeneity in nanoscale electrochemical processes and allow for many single nanoparticles to be measured in parallel, revealing relationships that are hidden using traditional electrochemical measurements. / Chemistry

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