A Highly Selective and Fluorescent Turn-on Method for Cu2+ Detection Based on Its Reaction with 3-Carboxyphenylboronic Acid

In this study, we developed a novel and facile fluorescent turn-on sensing method for the selective detection of Cu 2+ ions based on the specific oxidative reaction between Cu 2+ ions and 3-carboxyphenylboronic acid (3-CPBA). In this reaction, 3-CPBA was oxidized by Cu 2+ to form 3-hydroxybenzoic acid, which emitted strong fluorescence emission at 412 nm. The resulting product was characterized using comprehensive spectroscopic analyses, including proton nuclear magnetic resonance ( 1 H NMR), carbon-13 nuclear magnetic resonance ( 13 C NMR), and electrospray ionization mass spectrometry (ESI-MS). These analyses confirmed the formation of 3-hydroxybenzoic acid as the primary product. Under optimal conditions, the proposed method could detect Cu 2+ in the range of 0.1–3 µM with a detection limit of 10.2 nM. The developed method exhibited high sensitivity, ease of operation, practicality, and good selectivity toward Cu 2+ over other metal ions. Furthermore, the practical applicability of the method was validated by successfully detecting Cu 2+ in real water samples, with good recoveries of 94.0–105.0%. Graphical A fluorescence turn-on method for Copper ions (Cu 2+ ) detection via oxidative hydroxylation of 3-carboxyphenylboronic acid (3-CPBA) was developed. Under alkaline conditions, Cu 2+ converted non-fluorescent 3-CPBA into highly fluorescent 3-hydroxybenzoic acid (λ ex/e m = 315/412 nm). The method achieved a 10.2 nM detection limit with linear response (0.1–3 µM), superior selectivity over competing metal ions, and validated performance in environmental waters.