Portable colorimetric detection of copper based on enhanced peroxidase-like activity of MoO₃ nanobelts

Trace detection of copper ions with high specificity is critical for early warning indicators and public health governance due to its involvement in multiple physiological processes within the human body. Unlike previous research that was only based on the localized surface plasmon resonance (LSPR) properties of MoO_3-x, this work presents a novel colorimetric sensing platform exploiting the peroxidase-like activity for sensitive copper detection. This mechanism provides higher specificity than conventional methods through the specific coordination of Cu²⁺ with MoO₃, which forms a bond that facilitates electron transfer. Furthermore, Cu and Mo exhibit a synergistic catalytic effect. The strong substrate adsorption affinity of Cu, combined with the stable redox-active sites provided by Mo, results in an optimized electronic configuration and an accelerated catalytic process. This process enhances the generation of reactive oxygen species in the presence of H₂O₂, thereby catalyzing the oxidation of the 3,3',5,5'-tetramethylbenzidine (TMB) substrate with a colorimetric response. To enhance the analytical reliability and practical applicability, we employed a portable optical device for colorimetric signal analysis and a smartphone-based red-green-blue (RGB) colorimetric analysis platform. These methods show high sensitivity, with detection limits of 4.61 nM (colorimetry), 6.35 nM (portable device), and 9.91 nM (RGB analysis), significantly below the U.S. EPA regulatory limit (20 μM). Validation using real samples (wheat and corn) confirms the platform's robustness in environmental monitoring and food safety applications, offering a cost-effective, rapid and simple method for copper detection.