Glutathione-stabilized palladium nanozyme for colorimetric assay of silver(I) ions

Glutathione-capped Pd nanoparticles with a size of 1.4-3.5 nm are facilely synthesized for peroxidase nanomimetics. The molar ratio of [Na2PdCl4]/[GSH] greatly affects the physicochemical properties including particle sizes, surface charge states and enzymatic activities. The most efficient Pd-based nanozyme, consisting of approximately 57% metallic Pd-0 species with an average diameter of 2.6 nm, exhibits the Km value of 0.068 mM toward 3,3', 5,5'-tetramethylbenzidine and 156 mM toward hydrogen peroxide. Ag+ selectively binds to Pd-0 species through metallophilic interactions and induces an apparent aggregation of Pd nanoparticles. This is the first report that Ag+ significantly inhibits the peroxidase mimicking activity of Pd nanoparticles. A Pd-based nanozyme is employed to explore colorimetric detection of Ag+ with the limit of detection of 1.2 nM. This developed sensing system is potentially applicable for quantitative detection of Ag+ in drinking water as well as Ag nanoparticles in aqueous solution.