A highly selective and sensitive colorimetric sensor for iodide detection based on anti-aggregation of gold nanoparticles

In this study, a simple and rapid colorimetric iodide (I−) sensor based on the anti-aggregation of gold nanoparticles (Au NPs) was presented. This assay relied upon the distance-dependent optical properties of gold nanoparticles, the combination of mercapto-functionalized thymine on Au NPs, and the stronger affinity between I− and mercury ions (Hg2+). Hg2+ was employed as cross-linking agent for pairs of modified Au NPs by the coordination between Hg2+ and thymine. In the simultaneous presence of I− and Hg2+, the aggregation of Au NPs could not occur because of the preferential formation of HgI2 complex. Thus, the sensing of I− based on anti-aggregation of Au NPs was developed with the color of the Au NPs changing from blue to red, which was readily seen by the naked eye. The colorimetric sensor exhibited high sensitivity with a low detection limit of 10 nM. Notably, a highly selective recognition of I− was shown against other halogen anions (F−, Cl−, Br−). It was further proved that this simple and quick determination of iodide had possibilities for applying to environmental applications.