Rapid detection of hexavalent chromium using CuO/CN/LDH as an oxidase mimetic and the construction of a paper-based device

A ternary structure (CuO/CN/LDH) composed of LDH-anchored g-C3N4 nanosheets loaded with CuO nanoparticles was successfully constructed via hydrothermal and co-precipitation methods, and a colorimetric sensing platform for hexavalent chromium (Cr(VI)) detection was proposed. The engineered nanomaterial demonstrates significantly enhanced oxidase-mimetic activity in the presence of Cr(VI), enabling rapid catalytic oxidation of 3,3’,5,5’-tetramethylbenzidine (TMB) with distinct chromogenic response. Mechanistic investigations reveal that Cr(VI) facilitates the conversion of dissolved oxygen into superoxide anions via redox cycling, thereby accelerating TMB oxidation. The sensor exhibits exceptional analytical performance with high accuracy (recoveries of 97.3-103.8%) and sensitivity (detection limit of 25 nM) in aqueous sample analysis. The sensor demonstrated excellent selectivity against common interfering metal ions, as well as high stability (still above 95% for 8 weeks). Notably, an innovative paper-based analytical device was developed in conjunction with smartphone-assisted colorimetric detection, achieving on-site visual quantification of Cr(VI) within 15 min. This integrated system provides a field-deployable solution for environmental monitoring, combining operational simplicity with reliable detection capabilities. This study addresses the main limitations of Cr(VI) sensors, such as their dependence on complex instruments and poor stability of natural enzymes, and demonstrates low detection limits, excellent selectivity, and long-term stability. In addition, the proposed methodology advances current sensing technologies by merging nanomaterial engineering with portable detection platforms, demonstrating significant potential for heavy metal surveillance in water quality management. Based on this, this study also constructed a paper-based colorimetric detection sensor.