A Simple Assay for Ultrasensitive Colorimetric Detection of Ag(+) at Picomolar Levels Using Platinum Nanoparticles

In this work, uniformly-dispersed platinum nanoparticles (PtNPs) were synthesized by a simple chemical reduction method, in which citric acid and sodium borohydride acted as a stabilizer and reducer, respectively. An ultrasensitive colorimetric sensor for the facile and rapid detection of Ag(+) ions was constructed based on the peroxidase mimetic activities of the obtained PtNPs, which can catalyze the oxidation of 3,3’,5,5’-tetramethylbenzidine (TMB) by H(2)O(2) to produce colored products. The introduced Ag(+) would be reduced to Ag(0) by the capped citric acid, and the deposition of Ag(0) on the PtNPs surface, can effectively inhibit the peroxidase-mimetic activity of PtNPs. Through measuring the maximum absorption signal of oxidized TMB at 652 nm, ultra-low detection limits (7.8 pM) of Ag(+) can be reached. In addition to such high sensitivity, the colorimetric assay also displays excellent selectivity for other ions of interest and shows great potential for the detection of Ag(+) in real water samples.