Tailored functional colloids and interfaces for nanoparticle impact electroanalysis
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Nanoparticle impact electroanalysis (NIE) is a new electrochemical method under development for fundamental physicochemical studies of single nanoparticles (NPs) and potential applications in biosensing of single molecules with ultralow limits of detection. This dissertation introduces the tailored design, synthesis, characterization, and optimization of functional materials that comprise the foundation for the NIE detection strategy of interest, which is based on the principle of electrocatatlytic amplication (ECA). The investigations presented herein focus on two materials that function as the foundation in the ECA-NIE detection strategy: 1) the ultramicroelectrode (UME) used to contact these NPs individually from solution and 2) the NPs themselves, which are the primary focus of this dissertation. The specially designed materials described have helped to overcome major fundamental limitations associated with the ECA detection strategy and thus improve critical figures of merit for NIE. In Chapter 1, the incorporation of Hg as the UME material is shown to significantly improve signal-to-noise, reproducibility, and time resolution for the NIE platform. In Chapter 2, the fundamental problem of colloidal instability is addressed and rectified by experimentally guided systematic optimization of the ECA solution conditions, in turn providing the means to properly calibrate and theoretically model NP impact events in terms of NP size and rate of impact at the UME surface. Chapters 3 and 4 highlight the synthesis, characterization, and analytical application of bifunctional catalytic/magnetic Pt-decorated iron oxide NPs for NIE. The bifunctional NPs serve as essential tools to overcome fundamental limitations of mass transport, which is achieved by physical manipulation using an externally applied magnetic field focused at the UME detection surface. The incorporation of magnetophoretically focused and accelerated NP transport results in a significantly improved limit of detection in comparison to diffusion-limited NIE strategies. In Chapter 5 we return to the study of NP aggregation kinetics with NIE and discuss mechanistic insights into the physicochemical processes that most likely influence Pt NP colloidal stability. The methodologies described in this dissertation provide an experimental blueprint to help establish a solid physical/analytical foundation of this rapidly evolving field of research.