“Green” colorimetric assay for the selective detection of trivalent chromium based on Xanthoceras sorbifolia tannin attached to gold nanoparticles

Abstract

The colorimetric detection of heavy metal ions based on gold nanoparticles (GNPs) with a functionalized surface layer has received much attention due to their unique size and the dependence of their optical and electronic properties on the degree of aggregation. We developed a simple, environmentally friendly detection technique which uses GNPs functionalized with Xanthoceras sorbifolia tannin (XT) as a colorimetric probe for the selective detection of Cr³⁺ based on the aggregation-induced color change in the GNPs. In the synthesis of the XT-functionalized GNPs, XT simultaneously acts as a reducing and a stabilizing agent without requiring additional reagents or treatment. The XT-stabilized GNPs obtained are almost spherical, stable and water-soluble. The XT-stabilized GNPs can be used as a high-selectivity template to chelate with Cr³⁺; this chelation induces the aggregation of the GNPs, resulting in a color change from red to gray/purple within a few seconds. The proposed colorimetric sensor has been successfully applied to the detection of Cr³⁺ in tap water and river water. Compared with the current materials and methods for Cr³⁺ detection based on GNPs, this approach opens up a novel and environmentally friendly technique for the efficient detection of Cr³⁺.