Challenges and Opportunities of Tip-Enhanced Raman Spectroscopy in Liquids

Tip-enhanced Raman spectroscopy (TERS) is an emerging technique with a large number of potential applications in different fields such as chemistry, physics, biology, life sciences, and materials science. TERS in liquids offers nondestructive and label-free topographical and chemical imaging of molecules and chemical reactions under native conditions at a nanometer scale. It combines Raman spectroscopy with scanning probe microscopy, providing a unique combination of chemical information and high spatial resolution. The versatility of TERS increases even further if it is modified for simultaneous electrochemical measurements. This paper reviews the recent progress of TERS in liquid, with a focus on molecular structures, interfaces, and chemical reactions studied to date. For example, TERS studies revealed nanoscale chemical images of various molecules containing a benzene ring such as thiophenol or carbon nanotubes. Additionally, heterogeneous catalytic reactions at the solid–liquid interface were investigated in a new way to gain a deeper insight into electrochemical processes. Furthermore, TERS measurements expanded our knowledge of several redox compounds and enabled new insights into various chemical transformations. Despite substantial progress, TERS in liquids is not yet a routine measurement method, and there are still several challenges to solve before TERS can unleash its full potential.