Colorimetric assay of NO2- and mercury(II) through on-off strategy of the peroxidase-like Cu,Mo-CDs

Abstract

Abstract In this work, a copper-molybdenum doped carbon dots (Cu,Mo-CDs) with peroxidase-like (POD) activity was synthesized by using one-step microwave digestion method. The Cu,Mo-CDs + NO2− system can promote 3,3′,5,5′-tetramethylbenzidine (TMB) oxidize to become its blue oxidative product(oxTMB) due to the formation of ∙NO2 free radical. While Hg2+ was introduced into the system, the POD-like activity of Cu,Mo-CDs + NO2− system was inhibited by Hg2+ due to strong interaction and the electron transfer between Cu,Mo-CDs and Hg2+. The bioenzyme-free colorimetric assay based on Cu,Mo-CDs nanozyme is used for detection of NO2− and Hg2+, showing lower detection limit (LOD) of 1.63 µg/L for NO2−, 0.13 µg/L for Hg2+, respectively and good recovery from 90.79 to 108.90%. The work paves a new way to design a nanozyme-based colorimetric protocol for traces NO2− and Hg2+ residues in food analysis.