Investigating Nanoscale Electrochemistry with Surface- and Tip-Enhanced Raman Spectroscopy

Abstract

The chemical sensitivity of surface-enhanced Raman spectroscopy (SERS) methodologies allows for the investigation of heterogeneous chemical reactions with high sensitivity. Specifically, SERS methodologies are well-suited to study electron transfer (ET) reactions, which lie at the heart of numerous fundamental processes: electrocatalysis, solar energy conversion, energy storage in batteries, and biological events such as photosynthesis. Heterogeneous ET reactions are commonly monitored by electrochemical methods such as cyclic voltammetry, observing billions of electrochemical events per second. Since the first proof of detecting single molecules by redox cycling, there has been growing interest in examining electrochemistry at the nanoscale and single-molecule levels. Doing so unravels details that would otherwise be obscured by an ensemble experiment. The use of optical spectroscopies, such as SERS, to elucidate nanoscale electrochemical behavior is an attractive alternative to traditional approaches such as scanning electrochemical microscopy (SECM). While techniques such as single-molecule fluorescence or electrogenerated chemiluminescence have been used to optically monitor electrochemical events, SERS methodologies, in particular, have shown great promise for exploring electrochemistry at the nanoscale. SERS is ideally suited to study nanoscale electrochemistry because the Raman-enhancing metallic, nanoscale substrate duly serves as the working electrode material. Moreover, SERS has the ability to directly probe single molecules without redox cycling and can achieve nanoscale spatial resolution in combination with super-resolution or scanning probe microscopies. This Account summarizes the latest progress from the Van Duyne and Willets groups toward understanding nanoelectrochemistry using Raman spectroscopic methodologies. The first half of this Account highlights three techniques that have been recently used to probe few- or single-molecule electrochemical events: single-molecule SERS (SMSERS), superlocalization SERS imaging, and tip-enhanced Raman spectroscopy (TERS). While all of the studies we discuss probe model redox dye systems, the experiments described herein push the study of nanoscale electrochemistry toward the fundamental limit, in terms of both chemical sensitivity and spatial resolution. The second half of this Account discusses current experimental strategies for studying nanoelectrochemistry with SERS techniques, which includes relevant electrochemically and optically active molecules, substrates, and substrate functionalization methods. In particular, we highlight the wide variety of SERS-active substrates and optically active molecules that can be implemented for EC-SERS, as well as the need to carefully characterize both the electrochemistry and resultant EC-SERS response of each new redox-active molecule studied. Finally, we conclude this Account with our perspective on the future directions of studying nanoscale electrochemistry with SERS/TERS, which includes the integration of SECM w...

Advances in surface-enhanced vibrational spectroscopy at electrochemical interfaces

“…High-resolution chemical imaging of electrochemical interfaces is the next major step for this technique, which will allow us to correlate interfacial properties with surface topography at the nanoscale and ultimately with local atomic structure. Also, as highlighted in a recent review by Van Duyne and co-workers [163], the combination of TERS with electrochemical imaging techniques would mark a further leap forward, enabling localised electrochemical activity and surface chemistry to be probed simultaneously. The field of EC-SEIRAS has, understandably, not enjoyed the same level of attention as EC-SERS, but many of the recent developments in surface Raman scattering techniques could in principle be extended to IR absorption spectroscopy, so there is no doubt scope for further innovation.…”

Silver Nanoprism-Loaded Eggshell Membrane: A Facile Platform for In Situ SERS Monitoring of Catalytic Reactions

“…Noble metal nanoparticles, including gold and silver nanoparticles, are currently of great interest for their distinctive plasmonic properties and extensive research attention in near-field related applications, such as surface-enhanced spectroscopy [1,2], biomedicine [3,4], photonics [5,6], and biosensing [7,8]. Recently, metal nanoparticle-based catalysis has become an increasing area of research [9,10].…”

A metallic molybdenum dioxide with high stability for surface enhanced Raman spectroscopy

“…The nature of the substrate material is one of the most critical factors to determine the performance of SERS910. An ideal SERS substrate material should include the following characteristics: strong SPR effect, high stability, low cost and good versatility11. So far, Au nanostructures are the most frequently used substrate materials in SERS due to their very strong SPR effects and highly chemical and thermal stability12131415.…”