Creating, characterizing, and controlling chemistry with SERS hot spots.

In this perspective we discuss the roles of hot spots in surface-enhanced Raman spectroscopy (SERS). After giving background and defining the hot spot, we evaluate a variety of SERS substrates which often contain hot spots. We compare and discuss the differentiating properties of each substrate. We then provide a thorough analysis of the hot spot contribution to the observed SERS signal both in ensemble-averaged and single-molecule conditions. We also enumerate rules for determining the SERS enhancement factor (EF) to clarify the use of this common metric. Finally, we present a forward-looking overview of applications and uses of hot spots for controlling chemistry on the nanoscale. Although not exhaustive, this perspective is a review of some of the most interesting and promising methodologies for creating, controlling, and using hot spots for electromagnetic amplification.