Boron–Nitrogen Co-Doped Polymer Dots as a Metal-Free and Substrate-Free Fluorescent Nanozyme for Dual-Modal Monitoring of Catechol

The environmental persistence and carcinogenicity of catechol (CC) necessitate sensitive, portable detection methods beyond complex instrumentation. This work addresses this challenge by developing a novel metal-free fluorescent nanozyme, boron and nitrogen co-doped carbonized polymer dots (B,N-CPDs), via a facile one-pot hydrothermal synthesis using peach gum polysaccharide and 3-aminophenylboronic acid. Heteroatom co-doping optimizes electronic properties, enhancing both catalytic reactivity and specific recognition via electron-withdrawing phenylboronic acid moieties. The B,N-CPDs integrate intrinsic fluorescence with metal-independent peroxidase-like activity, enabling dual-modal (fluorescence/colorimetric) detection of CC without external substrates or labels. The fluorescence mode is exceptionally sensitive, with a detection limit of 0.25 nM across a wide linear range (0-72 μM). When coupled with smartphone-based analysis, the system achieves rapid, on-site dual-signal readout with low detection limits of 2.18 μM (fluorescence) and 4.5 μM (colorimetric), which surpass the performance of many existing techniques for CC detection. The platform demonstrates exceptional selectivity against interferents and high accuracy in environmental water samples (tap, lake, river, waste), with spike recoveries of 97.74-104.19% (RSD < 3.32%). This portable, eco-friendly sensing platform provides reliable cross-verified detection for real-time environmental CC monitoring.