Colorimetric speciation of Cr(III) and Cr(VI) with a gold nanoparticle probe

Gold nanoparticles (AuNPs) have frequently been explored for colorimetric probes for metal ions, including Cr(III), but probes capable of speciation of chromium, i.e., detection of both Cr(III) and Cr(VI), are seldom reported. In this work, by taking advantage of the coordination between Cr(III) and citrate, as well as the ligand effect of citrate for synthesis and stabilization of AuNPs, a colorimetric probe for Cr(III) detection based on citrate-capped AuNPs was reported. Cr(VI) was also detected after reduction to Cr(III). Speciation analysis of Cr(III) and Cr(VI) was thus performed. The citrate-capped AuNPs exhibited excellent selectivity toward Cr(III) over other common metal ions. Limits of detection for Cr(III) were 4 mu M and 0.3 mu M with the naked eye and UV-vis spectroscopic detection, respectively. The analytical performances for Cr(VI) were very much similar to those for Cr(III). The analytical potential of the proposed colorimetric speciation probe was evaluated for successful detection of Cr(III) and Cr(VI) in water samples, with spike-recoveries ranging from 96.7 to 106%.