Controlled plasmonic nanostructures for surface-enhanced spectroscopy and sensing.

After its discovery more than 30 years ago, surface-enhanced Raman spectroscopy (SERS) was expected to have major impact as a sensitive analytical technique and tool for fundamental studies of surface species. Unfortunately, the lack of reliable and reproducible fabrication methods limited its applicability. In recent years, SERS has enjoyed a renaissance, and there is renewed interest in both the fundamentals and applications of SERS. New techniques for nanofabrication, the design of substrates that maximize the electromagnetic enhancement, and the discovery of single-molecule SERS are driving the resurgence of this field. This Account highlights our group's recent work on SERS. Initially, we discuss SERS substrates that have shown proven reproducibility, stability, and large field enhancement. These substrates enable many analytical applications, such as anthrax detection, chemical warfare agent stimulant detection, and in vitro and in vivo glucose sensing. We then turn to a detailed study of the wavelength and distance dependence of SERS, which further illustrate predictions obtained from the electromagnetic enhancement mechanism. Last, an isotopic labeling technique applied to the rhodamine 6G (R6G)/silver system serves as an additional proof of the existence of single-molecule SERS and explores the dynamical features of this process. This work, in conjunction with theoretical calculations, allows us to comment on the possible role of charge transfer in the R6G/silver system.