A single-nanozyme colorimetric array based on target-induced differential surface passivation for quantification and discrimination of Cl, Br and I ions.

Abnormal levels of halide ions in drinking water have enormous threats to human health, and thus designing reliable and sensitive methods to quantify and distinguish these ions becomes extremely crucial. Herein, we develop a single-nanozyme colorimetric array based on target-induced differential surface passivation for the quantification and discrimination of Cl, Br and I ions. Silver citrate (AgCit) is designed as an oxidase mimic to efficiently catalyze the 3,3',5,5'-tetramethylbenzidine (TMB) chromogenic reaction. When halide ions (Cl, Br and I) are present, due to their different precipitation interactions with the Ag(Ⅰ) entity in AgCit, they can passivate the active surface of the nanozyme to various degrees, resulting in the inhibited TMB chromogenic reaction differentially. According to this principle, simple and efficient quantitative detection of Cl, Br and I ions was achieved, with all the detection limits down to the nM level. By employing AgCit as a single sensing element, a nanozyme catalysis-based colorimetric array was further established, and both individual and mixed ions were successfully distinguished by integrating the array with principal component analysis. Accurate identification of unknown samples was also verified via a double-blind protocol, indicating potential applications of the array in practice.