Humidity-responsive nanocomposite of gold nanoparticles and polyacrylamide brushes grafted on Ag film: synthesis and application as plasmonic nanosensor

A general stepwise strategy for the preparation of new humidity-responsive plasmonic nanosensor was described for the first time, based on Ag film functionalization by polyacrylamide (PAAM) brushes via surface-initiated atom transfer radical polymerization (SI-ATRP) method and then assembled with gold nanoparticles (Au NPs). We designed by this way a new plasmonic device made of Au NPs embedded in a humid vapor responsive polymer layer on Ag film and extensively characterized by surface-enhanced Raman scattering (SERS). When the relative humidity (RH) is above 50%, the number of plasmonic hotspots decreases, causing SERS signal reduced noticeably, for the volume expansion of PAAM brushes varied the nano-gap between closely spaced Au NPs, and between Au NPs and Ag film. The reversible optical properties of the prepared nanocomposite tuned by RH were probed through SERS using 4-mercaptopyridine (4-Mpy) as a molecular probe, and the decrease of the RH reversibly induces a significant enhancement of the 4-Mpy SERS signal. By means of the high reversibility, the RH responsive nanocomposite developed in this paper provides a dynamic SERS platform and can be applied as plasmonic nanosensor which is proved to be stable for at least two months.