Monolithic porous gold nanostructures as surface-enhanced Raman spectroscopy substrates for molecular and biosensing

Surface-enhanced Raman spectroscopy (SERS) has been widely used for high-sensitivity molecular detection and identification. It is advantageous for a SERS substrate to have a large surface-to-volume ratio from the standpoint of high density “hot spots” and optical sampling efficiency. In this paper, we show that monolithic porous gold nanostructures such as nanofilms and nanodisks can be effective SERS substrates with large surface area. The average enhancement factor of the nanodisk and nanofilm substrates have been determined using benzenethiol self-assembled monolayers to be ~100 million and 0.5 million, respectively. Variability on the order of 40% has been observed by large area SERS mapping. A single nanodisk coated with benzenethiol self-assembled monolayer (~10 attmoles) can provide SERS spectrum with a signal-to-noise ratio ~400, resulting in an estimated detection limit in the range of zeptomoles.