Ultrastable, Uniform, Reproducible, and Highly Sensitive\nBimetallic Nanoparticles as Reliable Large Scale SERS Substrates

Abstract

A strong interest exists in developing\nsurface-enhanced Raman spectroscopy\n(SERS) substrates that uniformly enhance Raman signals of chemical\nand biological molecules over large scales while reaching the detection\nlimit of trace concentrations. Even though the resonant excitation\nof localized surface plasmons of single or assembled metallic nanoparticles\nused in SERS substrates can induce large electromagnetic fields, these\nsubstrates display a SERS activity which suffers from poor reproducibility,\nuniformity, and stability, preventing them from being reliable for\napplications. In this work, we have developed self-supported large\nscale Ag/Au bimetallic SERS-active substrate with a high density of\nnanoparticles and uniform hot spots. The resultant substrates are\nvery stable under ambient conditions, providing unchanging Raman enhancement\nsignals even after one year of fabrication, due to the protective\nAu shell on the bimetallic nanoparticles. The Ag/Au bimetallic substrate\nexhibits remarkable SERS enhancement for nonresonant molecules, permitting\nthe detection of trace concentrations reaching 10^–13 mol/L.