Microfabricated electrode arrays as a tool for the investigation of diffusion limited electrochemistry at the nanoscale

Electrochemistry at the nanoscale is a fascinating research discipline, as it is of great importance for industrial applications and furthermore offers new insight into physical and chemical phenomena at a very fundamental level. Silver nanoparticles for example are widely used as anti microbial coating. The unique properties of metal nanoparticles, like a high surface charge and fastmass transport, allows to use them for biosensing applications. The presented work investigates the suitability microelectrodes for amperometric particle detection. By the use of an array of microelectrodes, the detection limit could be improved by an order of magnitude in comparison to single microelectrode sensors. The measurement results are compared to random walk simulations and the limiting factor of the detection system could be identifed as particle adsorption. To enhance the understanding of the detection mechanism, where silver is oxidized to silver chloride, the infuence of the electrolyte on the particle detection is investigated. For low chloride concentrations the oxidation process becomes limited by the diffusive mass transport of chloride. This makes the actual dynamics of the oxidation event of single nanoparticles accessible with our measurement setup. By comparison to our measurement data we show that the time-dependent oxidation current can be described by an analytical model. Silver nanoparticles can be used as tracer for biosensing applications. To investigate the suitability for amperometric detection in biosensing, the interaction of silver nanoparticles with the electrode surface in presence of organic thiol molecules is investigated. To this end the infuence of self assembled monolayers of thiols which feature different length and different functional groups on nanoparticle-electrode interaction is measured. Finally the infuence of adsorption processes on the performance of redox cycling sensors in investigated. Electrochemical redox cycling sensors feature an intrinsic amplifcation by repetitive oxidation and reduction of the same molecules at two contrarily biased electrodes. By random walk simulations the infuence of dynamic adsorption of the redox molecules on the sensor's response time is investigated. Adsorption processes can also be used for an indirect detection where adsorbed analyte molecules infuence the performance of the sensor. This is exemplary investigated by random walk simulations for a nonporous redox cycling device