Sensing Interfacial Non-Faradaic and Faradaic Processes via Plasmonic-Enhanced optical processes with Nano-Optoelectrodes

Abstract

Metallic nanostructures that sustain surface plasmon resonances are capable of strongly localizing electromagnetic fields, thereby intensifying radiative emission processes originating from plasmonic "hotspot" regions. This nanoplasmonic metal luminescence not only constitutes a significant background component in surface-enhanced Raman spectroscopy (SERS) measurements, but also offers functional utility in applications such as bioimaging, nanoscale thermometry, and real-time monitoring of chemical transformations. Although interest in this phenomenon has grown, its modulation under applied electrochemical potentials remains insufficiently explored. In particular, electrochemical surface-enhanced spectroscopy (EC-SERS) has traditionally treated the voltage-dependent spectral background arising from nanoplasmonic luminescence as a secondary effect, largely due to the lack of a comprehensive mechanistic framework and challenges associated with reproducible measurements. Consequently, potentially valuable information embedded in this background signal has been underutilized. In this thesis, we integrate systematic experimental investigations with theoretical modeling to elucidate the dynamic behavior of nanoplasmonic metal linear and nonlinear luminescence under both Faradaic and non-Faradaic modulation. By employing a series of engineered nano-optoelectrodes, we simultaneously probe luminescence responses including electronic and molecular vibrational Raman signals and nonlinear optical emission generated at plasmonic hotspots located at electrode–electrolyte interfaces. This combined approach provides new insight into the coupling between optical and electrochemical processes at the nanoscale. Overall, this thesis establishes a foundation for leveraging nanoplasmonic luminescence as an active signal transduction mechanism, with implications for optical voltage sensing, hybrid optoelectronic interfacing, and high-resolution interrogation of interfacial electrochemical dynamics.