Interface-Induced Ag Monolayer Film for Surface-Enhanced Raman Scattering Detection of Water-Insoluble Enrofloxacin

Water-insoluble molecules usually show poor surface-enhanced Raman scattering (SERS) signals, because they are hardly adsorbed on the surface of most commonly used SERS substrates, such as aqueous Ag or Au colloids. In this work, a highly sensitive and reproducible Ag monolayer film (Ag MLF) SERS substrate prepared by self-assembly of Ag nanoparticles (Ag NPs) on water/oil interface can realize the trace SERS detection of water-insoluble enrofloxacin. The positively charged phase transfer catalyst can transfer the negatively charged Ag nanoparticles in aqueous solution to the water/oil interface. At the same time, the water-insoluble enrofloxacin can also be attracted to the interface because of its lipophilic group. The type/volume of the oil phase and phase transfer catalyst and the vortex mixing time were all optimized to maximize the SERS effect of Ag MLF. Results showed that trace water-insoluble enrofloxacin can be identified by Ag MLF and its detection sensitivity was significantly improved. The proposed novel Ag MLF can be further applied to detect other water-insoluble molecules in SERS.