Colorimetric assay for the simultaneous detection of Hg2+ and Ag+ based on inhibiting the peroxidase-like activity of core–shell Au@Pt nanoparticles

In this study, peroxidase-mimicking core–shell Au@Pt nanoparticles (Au@Pt NPs) were synthesized, and both Hg2+ and Ag+ were found to intensively inhibit the catalytic activity of the Au@Pt NPs. The interactions between the two metal ions and Au@Pt NPs were analyzed through characterization by TEM, DLS, EPR and XPS, etc. Based on the inhibition of both Hg2+ and Ag+ toward the catalytic activity of the Au@Pt NPs and the shielding of sodium dodecyl sulfate (SDS) toward interfering metal ions, a highly sensitive and selective colorimetric assay for Hg2+ and Ag+ was developed. In addition, L-cysteine can be used to mask Hg2+ in the presence of Ag+; therefore, a specific detection of Ag+ ions can be accomplished by this Au@Pt NP-based assay. The limits of detection (LODs) for Hg2+ and Ag+ are 3.5 nM and 2.0 nM, respectively. The linear ranges for detecting Hg2+ and Ag+ are from 10 nM to 200 nM and from 5.0 nM to 100 nM, respectively. Moreover, the colorimetric assay is highly selective toward Hg2+ and Ag+ over other common metal ions. This work demonstrates that the optimization of metal nanoparticle preparation and surface modification play very important roles in developing metal ion sensing based on metal NP enzyme mimics. In addition, the metallic nanozyme based colorimetric method here demonstrates advantages in practical applications as it is low-cost, simple, and highly sensitive and selective, although it needs a two-step reaction.