Pore evolution and size effect of nanoporous silver on SERS for malachite green detection

Abstract

The nanoporous silver (NPS) films with the average pore size ranging from 51 to 246 nm were synthesized by dealloying co-sputtered AgxAl100-x (x = 30–56 at%) precursor films in 1 M HCl for 30–120 min. The structure of the NPS films, the dissociation of Al, and the aggregation of Ag were evaluated by field emission scanning electron microscopy as a function of dealloying time. The results showed that the pore size first decreased as the dealloying time increased, followed by pore coarsening, regardless of the relative density of NPS films. The finite-difference time-domain (FDTD) simulation further indicated that the smaller the nanopores, the higher the hot-spot area and surface electric field. As the average pore size of NPS film decreased to 51 nm, the enhanced Raman intensity of rhodamine 6G (R6G) using the NPS film as substrate was at least two orders higher than that using pure Ag film. Meanwhile, the detection limit of malachite green, a wildly used chemical in aquaculture, was 10-5 M with the enhancing factor 1.58 × 105.