Photoelectrochemical imaging of gold nanoparticles by light-activated electrochemistry
The concept of light-activated electrochemistry (LAE) on Si was developed as a single-wire electrode array where a light pointer created localized conductive channels on a monolithic monolayer-terminated Si electrode and allowed undertaking spatially-resolved faradaic electrochemistry on the surface of Si electrode at desired locations. Herein, LAE was expanded to an electrochemical imaging technique. In the original work published for LAE and the follow-up studies, the Si electrode was modified and investigated with redox species, such as ferrocene or anthraquinone, attached to a monolayer modified electrode, which limits the working potential of the system, in particular for imaging applications. In this thesis, to overcome this limitation, instead of redox species, AuNPs were attached to the monolayer (SAM) and redox species were dissolved in the electrolyte. Then the behaviour of the construct was studied on Si electrodes using a variety of doping level and types as well as dissolved redox species with various charges and oxidation states. Most favourable results were obtained using an n-type Si for photo oxidation of Co(phen)32+, which is a positively charged species undergoing oxidation initially. Favourable means before attaching AuNPs, the NH2-terminated electrode is passivated against electron transfer to/from Co(phen)32+ in the dark and light, while upon attachment of AuNPs, electron transfer is restored under illumination and is negligible in the dark. Finally, the developed electrode and knowledge were implemented to record a photoelectrochemical image of a AuNP island on an NH2-terminated electrode using a state-of-the-art light projector. The developed imaging technique significantly enhances the versatility of electrochemical imaging compared to the conventional methods like scanning electrochemical microscopy, that employ a mechanically moving tip with predefined geometry, limited scanning speeds and intricate positioning. Whereas, the LAE-based technique developed in this thesis takes advantage of a high-speed light projector, which is versatile in terms of light spot shape, size, and scanning speed, therefore, making it a potential high-speed high throughput electrochemical imaging technique.
Light-activated electrochemistry, Photoelectrochemistry, Nanotechnology, Semiconductor, Gold nanoparticles, Electron transfer
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