Multifunctional Fluorescent Schiff Base Probe Derived From Chlorosalicylaldehyde for Selective Detection of Proteins, Nitroexplosives, Metal Ions and Antibiotics.

Multifunctional fluorescent chemosensors capable of detecting chemically diverse analytes using a single molecular platform are increasingly valuable for environmental monitoring and biomedical analysis due to reducing analytical cost, time, and complexity. However, most Schiff base probes are limited to single-analyte detection or operate through a single sensing mechanism. In this study, a new Schiff base probe, ClSNP, synthesized from 3,5-dichlorosalicylaldehyde and N-phenyl-o-phenylenediamine, exhibited a fluorescence "turn-off" response toward Cu2 + and Co2 + ions in a CH3CN/H2O medium with high selectivity even in the presence of competing metal ions. Job's plot analysis confirmed a 1:1 binding stoichiometry, with detection limits of 1.79 and 3.40 µM for Cu2 + and Co2+ ions, respectively, both below WHO-permitted levels. Additionally, it selectively detected picric acid (PA) in THF with a detection limit of 2.49 µM and responded to antibiotics, including nitrofurantoin and metronidazole. It showed a "turn-on" fluorescence enhancement at 460 nm upon binding with bovine serum albumin (BSA) with a detection limit of 1.28 µM, attributed to restricted intramolecular rotation, supported by a molecular docking study. The probe demonstrated high sensitivity, good selectivity, and real-sample applicability, offering a versatile, cost-effective, and mechanism-switchable sensing platform.