Synthesis of Dual-Functional Ag/Au Nanoparticles Based on the Decreased Cavitating Rate under Alkaline Conditions and the Colorimetric Detection of Mercury(ii) and Lead(ii)

By increasing the pH value of the reaction solution and introducing a small amount of ascorbic acid, Ag/Au nanoparticles with small tips and two surface plasmon resonance (SPR) modes have been prepared. The formation of the two SPR modes results from the different shell and core Au/Ag ratios, which relies on the enhanced dealloying rate of the shell and the weakened cavitating rate of the core under high pH conditions. Then, these Ag/Au nanoparticles have been used in the ultrasensitive detection of Hg2+ and Pb2+ based on the resultant absorption intensity decrease of peaks I and II, which originates from the specific dissolution of Ag and the accelerated speed of the reaction between Na2S2O3 and Au, respectively. The results showed an excellent limit of detection (LOD) of 5 nM for Hg2+ and 1.4 nM for Pb2+, and linear ranges from 30 to 400 nM and from 3 to 180 nM, respectively. Meanwhile, we believe that these bimetallic nanoparticles have widespread applications in sensing and modulating pH based on the dealloying rate of the shell and the cavitating rate of the core which can be extended to the synthesis of other dual-functional metallic nanoprobes.