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Metallic nanostructures supporting surface plasmon modes can concentrate optical fields, and enhance luminescence processes from the metal surface at plasmonic hotspots. Such nanoplasmonic metal luminescence contributes to the spectral background in surface-enhanced Raman spectroscopy (SERS) measurements and is helpful in bioimaging, nano-thermometry, and chemical reaction monitoring applications. Despite increasing interest in nanoplasmonic metal luminescence, little attention has been paid to investigating its dependence on voltage modulation. Also, the hyphenated electrochemical surface-enhanced Raman spectroscopy (EC-SERS) technique typically ignores voltage-dependent spectral background information associated with nanoplasmonic metal luminescence due to limited mechanistic understanding and poor measurement reproducibility. Here, we report a combined experiment and theory study on dynamic voltage-modulated nanoplasmonic metal luminescence from hotspots at the electrode-electrolyte interface using multiresonant nanolaminate nano-optoelectrode arrays. Our EC-SERS measurements under 785 nm laser excitation demonstrate that short-wavenumber nanoplasmonic metal luminescence associated with plasmon-enhanced electronic Raman scattering (PE-ERS) exhibits a negative voltage modulation slope (up to ≈30 % V-1) in physiological ionic solutions. Furthermore, we have developed a phenomenological model to intuitively capture plasmonic, electronic, and ionic characteristics at the metal-electrolyte interface to understand the observed dependence of the PE-ERS voltage modulation slope on voltage polarization and ionic strength. The current work represents a critical step toward the general application of nanoplasmonic metal luminescence signals in optical voltage biosensing, hybrid optical-electrical signal transduction, and interfacial electrochemical monitoring. 

Abstract In situ monitoring of short‐lived transition states (TSs) is crucial for understanding electrochemical reaction mechanisms but remains challenging. Conventional electrochemical surface‐enhanced Raman spectroscopy (EC‐SERS) primarily provides vibrational information, with limitations in hotspot reproducibility and often overlooking electronic information associated with TSs. This study introduces a dual‐channel EC‐SERS strategy using nanolaminate nano‐optoelectrode (NLNOE) devices, integrating plasmon‐enhanced vibrational Raman scattering (PE‐VRS) and plasmon‐enhanced electronic Raman scattering (PE‐ERS) to concurrently probe TS dynamics within electrically connected plasmonic nanocavities. Using theAgCl(s) +e⁻⇌Ag(s) +Cl⁻(aq) redox system, this approach distinct PE‐VRS and PE‐ERS signatures of the (AgCl)^*TS. Notably, a significant increase in PE‐ERS signals concurrent with (AgCl)^*TS emergence, characterized by filled bonding and unoccupied antibonding orbitals with negligible energy gaps. This enhanced PE‐ERS signal correlates with increased (AgCl)^*TS polarizability, leading to amplified PE‐VRS signals due to enhanced electron cloud distortion. By modulating Cl⁻ ion concentrations via electrolyte composition (1× PBS and 1× PBS‐equivalent KH₂PO₄) while maintaining constant total ion concentration, the competition between Ag/AgCl and Ag/AgH₂PO₄ redox reactions within Ag nanolayers is influenced. These results demonstrate the capability of dual‐channel EC‐SERS to distinguish interfacial redox reactions based on distinct electronic and vibrational signatures associated with covalent and ionic bond characteristics.