Tunable laccase-mimicking metal covalent organic framework nanozyme: A new strategy with two signal-reading modes for the visual detection of Cr3+ and Al3+

A stable Cu-based MCOFs with outstanding laccase-mimicking nanozyme activity was synthesized. • Steady-state kinetic assays verify the superior substrate affinity and faster catalytic rate of Cu₃-TAPT COF. • A two signal-reading-mode colorimetric sensor was constructed for detection of Cr 3+ and Al 3+ . • The sensing platform can be successfully applied for real water samples. Cr 3+ and Al 3+ are toxic metal ions widely existing in environmental water, and traditional detection methods cannot meet the demand for on-site analysis. Metal covalent organic frameworks (MCOFs) are promising nanozyme candidates, which overcome the defects of conventional nanozymes by virtue of ordered structure, good stability and uniformly distributed active sites. In this study, Cu 3 -TAPT COF, a typical MCOF nanozyme with high stability and excellent laccase-mimicking activity was fabricated. Relying on the differential inhibitory effects of Cr 3+ and Al 3+ on its catalytic activity, an inhibition-based colorimetric platform was established for their separate detection. This sensing system integrates naked-eye visible color variation, quantitative absorbance signal at 510 nm, and smartphone image capture for portable on-site readout. The method validation results demonstrated that the limits of detection (LODs) were 0.30 μM for Cr 3+ and 0.22 μM for Al 3+ . The overall recoveries of all spiked groups for the two ions in three actual water samples (river water, seawater, and lake water) ranged from 93.41% to 109.8%. This work validates the great potential of laccase-mimicking MCOF nanozymes in environmental monitoring and sheds new light on the fabrication and practical exploitation of MCOF-derived nanozymes. Download: Download high-res image (116KB) Download: Download full-size image