pH-switchable multi-enzyme-like activities of Bi12Co0.6O18.8-AuNPs nanozyme: An electrochemical-colorimetric dual-mode aptasensor for ultrasensitive Cd2+ detection in rice.

The severe health risks associated with cadmium-contaminated food necessitate the development of accurate and rapid detection technologies. Herein, a novel pH-switchable multi-enzyme activity Bi12Co0.6O18.8-AuNPs is designed to construct a dual-mode aptasensor for the rapid and reliable detection of Cd2+. This nanozyme exhibits pH-modulated catalytic behaviors, demonstrating peroxidase-like activity under acidic conditions (pH 4) to catalyse the H2O2-mediated oxidation of 3,3',5,5'-tetramethylbenzidine for visual colorimetric detection, while switching to catalase-like activity at slightly alkaline conditions (pH 8) to decompose H2O2 into O2, thereby generating a measurable electrochemical signal. Benefiting from the collaborative enhancement mechanism of the dual-mode strategy through cross-validation and the high specificity of aptamer recognition, the sensor achieves highly precise and reliable detection of Cd2+. The sensor shows ultra-sensitive detection with limits of detection of 9.23 pg/mL (colorimetric) and 0.43 pg/mL (electrochemical). Its successful application in real rice samples confirms its practical utility for food safety monitoring.