Simple and selective colorimetric detection of hypochlorite based on anti-aggregation of gold nanoparticles

By fully utilizing the strong oxidation property of hypochlorite (OCl−), we develop a facile colorimetric approach for the detection of hypochlorite with unmodified gold nanoparticles (AuNPs). This method based on the anti-aggregation of AuNPs takes advantage of the cross-linking capability of dithiothreitol (DTT). DTT could cause AuNPs to aggregate owing to the strong covalent SAu bond, with a clear color change of solution from red to blue. In the presence of hypochlorite, however, the thiol groups would readily be oxidized, and thus a red solution was observed after the subsequent addition of Au suspension owing to incapability of the oxidative derivatives of being chemisorbed on the negatively charged AuNP surface. With this colorimetric method, 2 μM of OCl− can be easily visualized by naked eye within 5 min. We applied this method to test the hypochlorite level in real water samples and satisfactory results were obtained. This sensitive and selective colorimetric assay might provide a convenient approach to detect OCl−/HOCl in various water samples.