Effects of Ions on Core-Shell Bimetallic Au@Ag NPs for Rapid Detection of Phosalone Residues in Peach by SERS

The sensitivity of surface-enhanced Raman spectroscopy (SERS) extremely relies on experimental parameters including pH and aggregating agents. Using Au@Ag nanoparticles (NPs) with 26 nm Au core size and 6 nm Ag shell thickness as the substrate, the effect of cationic (Ca2+, K+, Na+) and anionic (Cl-, Br-) aggregating agents was investigated on the SERS detection of phosalone. The optimum concentrations of the aggregating agents in relation to the maximum SERS intensity differed broadly from 1 x 10(-2) mol/L for CaBr2 to 1 x 10(1) mol/L for KCl. Both anions and cations greatly affected the SERS enhancement. With employing Br- as the anion, Ca2+ and K+ showed the maximum SERS intensities for phosalone, while using Ca2+ as the cation, Br- produced the maximum SERS enhancement. Among these aggregating agent combinations, the maximum SERS enhancement was achieved by employing 1 x 10(-2) mol/L CaBr2 at pH 3.0. The detection limits of phosalone in standard solution and peach were 0.02 mg/L and 0.2 mg/kg, respectively. This study demonstrated that the Au@Ag NP-based SERS approach could be used as a sensitive, rapid, and simple method for detecting trace contaminants in food matrices.