Citrate-Capped Platinum Nanoparticle as a Smart Probe for Ultrasensitive Mercury Sensing

An easily prepared platinum nanoparticle (PtNP) probe for the sensitive and selective detection of Hg2+ ions is developed here. The PtNPs with an average size of approximately 2.5 nm were prepared by a reduction method with sodium borohydride and trisodium citrate serving as reductant and stabilizer, respectively. The resulting PtNPs could catalyze the reduction of Hg2+ by surface-capping citrate. The effect of Hg2+ uptake implies amalgam formation, which leads to remarkable inhibition of the peroxidase-like activity of citrate-capped PtNPs. On the basis of this effect, a colorimetric mercury sensor was established through the use of citrate-capped PtNPs to catalyze the colorimetric system of 3,3′,5,5′-tetramethylbenzidine (TMB) and H2O2. The high specificity of the Hg–Pt interaction provides the excellent selectivity for Hg2+ over interfering metal ions. The sensitivity of this smart probe to Hg2+ is extremely excellent with a limit of detection (LOD) as low as 8.5 pM. In view of these advantages, as well as the cost-effectiveness, minimized working steps, and naked-eye observation, we expect that this colorimetric sensor will be a promising candidate for the field detection of toxic Hg2+ ions in environmental, biological, and food samples.