Colorimetric sensing of copper ions based on the anti-aggregation of unmodified silver nanoparticles in the presence of 1,4-dithiothreitol

Abstract

Copper is an essential element for the regulation of many biological processes, however, an excess of Cu²⁺ is considered to be toxic to human health. It is highly desirable to develop a simple, rapid, sensitive, and selective assay for Cu²⁺ recognition. Herein, a colorimetric sensor for copper ions with high selectivity and sensitivity using unmodified sliver nanoparticles (Ag NPs) is presented. 1,4-Dithiothreitol (DTT) can cause the Ag NPs to aggregate, with a clear color change of solution from yellow to deep green being visualized. In contrast, in the presence of O₂, Cu²⁺ can catalyze the oxidation of DTT. And the thiols of DTT would readily be converted to disulfide bonds. An increase in the concentration of Cu²⁺ alleviated DTT-induced Ag NP aggregation by decreasing the number of free thiol groups in DTT, and the solution color changed from deep green to yellow. With this strategy, 1 μM of Cu²⁺ can be recognized within 30 min at room temperature by naked eye observation. Since the Cu²⁺-catalyzed oxidation reaction and the colorimetric response are two separate phenomena, this approach features the use of pristine Ag NPs in an assay, making it a convenient method for the sensing of Cu²⁺ when compared with those utilizing chemically modified Ag NPs. Additionally, the proposed method has good selectivity to Cu²⁺ in the presence of other common metal ions. Taken together, these advantages make this assay simple and robust and therefore promising for on-site water testing.