Protamine-gold nanoclusters as peroxidase mimics and the selective enhancement of their activity by mercury ions for highly sensitive colorimetric assay of Hg(II).

We certify that protamine-gold nanoclusters (PRT-AuNCs) synthesized by one-pot method exhibit peroxidase-like activity. The catalytic activity of PRT-AuNCs followed typical Michaelis-Menten kinetics and exhibited higher affinity to 3,3',5,5'-tetramethylbenzidine (TMB) as the substrate compared to that of natural horseradish peroxidase. Meanwhile, we found that Hg(II) could dramatically and selectively enhance the peroxidase-like activity of PRT-AuNCs, and the enhanced mechanism by Hg(II) was demonstrated to be generation of the cationic Au species and the partly oxidized Au species (Auδ+) by Hg2+-Au0/Au+ interaction. Based on this finding, quantitative determinations of Hg(II) via visual observation and absorption spectra were achieved. The proposed strategy displays high selectivity that arises from the strong aurophilic interaction of mercury towards gold. Moreover, the developed method is highly sensitive with a wide linear range and low detection limit of 1.16 nM. This strategy is not only helpful to develop effective nanomaterials-based artificial enzyme mimics but also irradiative to discover new applications of artificial mimic enzymes in bio-detection, medical diagnostics, and biotechnology. Graphical abstract Protamine-gold nanoclusters (PRT-AuNCs) synthesized by one-pot method exhibit peroxidase-like activity. Hg(II) can stimulate the peroxidase-like activity of PRT-AuNCs selectively, enhancing their ability to catalyze the chromogenic reaction of TMB by H2O2.