Cu(Ⅱ) triggering redox-regulated anti-aggregation of gold nanoparticles for ultrasensitive visual sensing of iodide

In this study, we proposed a novel anti-aggregation of gold nanoparticles (AuNPs) strategy for colorimetric sensing of iodide ions (I^-) regulated by the redox reaction between the target ions and the ion cross-linking agent. Cu²⁺ as interlinking ion can induce aggregation of arginine capped AuNPs (Arg-AuNPs) due to the formation of Arg-Cu²⁺-Arg analogous structure resulting from the chelation between Cu²⁺ and arginine, with a clear color change of solution from red to blue. In the presence of I^-, however, Cu²⁺ would be readily reduced owing to the formation of CuI, AuNPs underwent a transformation from an aggregation to a dispersion state depending on the concentration of I^-, leading color changes from blue to red. The corresponding color variation in the process of anti-aggregation of AuNPs can be monitored through UV-vis spectrophotometer or by the naked-eye, making quantitative analysis of I^- feasible in a convenient colorimetric or visual way. The assay only took 5 min, showing high sensitivity with a lowest detectable concentration of 10 nM and excellent selectivity for I^- over other anions tested, which was successfully applied for the detection of I^- in drinking water and table salt samples.