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%.