Convenient and sensitive colorimetric detection of melamine in dairy products based on Cu(ii)-H 2 O 2 -3,3',5,5'-tetramethylbenzidine system.

The illegal adulteration of melamine in dairy products for false protein content increase is a strong hazard to human health. Herein, a simple and sensitive colorimetric method was developed for the quantification of melamine in dairy products based on a Cu 2+ -hydrogen peroxide (H 2 O 2 )-3,3',5,5'-tetramethylbenzidine (TMB) system. In this strategy, Cu 2+ exhibits peroxidase-like activity and can catalyze the oxidation of TMB to oxidized TMB (oxTMB) in the presence of H 2 O 2 with a blue colour change of the solution. However, the presence of melamine quickly interacts with H 2 O 2 leading to the consumption of H 2 O 2 and thus strongly hinders the oxidation of TMB. Under the optimal conditions, the absorbance change of oxTMB has a linear response to the concentration of melamine from 1 to 100 μM with a detection limit of 0.5 μM for melamine. The proposed method has many merits including more simplicity, good selectivity, and more cost-effectiveness without using any nanomaterials. The method was further successfully applied to detect melamine in dairy products including milk and infant formula powder.