Smartphone-Aided Colorimetric Assay: Enhanced Peroxidase Mimicking Activity of Quasi Cube-Like 2D-Co-MOF/CN Label-Free Nanozyme for Selective/Visual Recognition of 4,4′-(propane-2,2-diyl)diphenol

To ensure environmental safety, it is essential to monitor bisphenol A (BPA), as it poses health hazards. In this study, we report a novel, sustainable binary 2D Co-MOF/CN nanozyme that functions as a bipurpose material with both peroxidase-mimic activity and BPA-specific detection capability. The Co²⁺ sites and sp² hybridized carbon demonstrate remarkable Fenton-like reactions, effectively promoting the transformation of 4,4'-diamino-3,3',5,5'-tetramethylbiphenyl (TMB) into oxidized TMB. The Co²⁺ sites in the binary 2D-Co-MOF/CN facilitate the capture of BPA via cobalt-O-H bonding and electrostatic interactions, hence restricting the transfer of e^- between 2D-Co-MOF/CN and hydrogen peroxide. Thus, TMB oxidation diminishes and alters the color from a strong blue to pale color, allowing for a visual detection of BPA. A robust linear association has been established between the BPA concentration and the absorbance intensity (λ_abs = 652 nm), with a detection limit of 2.1 nM. These limitations are far lower than the European Commission Environment (ECE) criteria. The system was further integrated into a smartphone-assisted platform using RGB color analysis for real-time on-site BPA monitoring. This demonstrated an efficient selectivity and efficacy with actual water samples. This research introduces a novel colorimetric and smartphone-adaptable innovative sensing platform for the visual detection of BPA using a multifunctional nanozyme. The multifunctional nanozyme not only enhances detection performance but also supports portable, green, and cost-effective monitoring strategies for practical environmental applications.