Regulatory-compliant detection of tetracycline food contaminants: A polyindole-based chemosensoric approach for food safety monitoring and toxicological risk mitigation.

The widespread contamination of tetracycline (TC) in aquatic environments and food chains poses significant risks to human health and ecosystem sustainability, necessitating the development of rapid, sensitive detection methods. Herein, we report polyindole (PIN) fluorescent sensor for highly selective TC detection. PIN exhibited a quantum yield of 0.27 in ethanol with characteristic blue emission at 428 nm upon excitation at 350 nm. Under optimized conditions (H2O/EtOH = 1:1, pH 7), PIN demonstrated exceptional selectivity and sensitivity toward TC over various interfering antibiotics and metal ions through fluorescence quenching. The sensor displayed a linear detection range of 0.05-7.3 μM with a remarkable limit of detection of 2.3 nM, achieving a binding constant of 1.08 × 105 M-1 with TC. Time-correlated single photon counting analysis revealed a static quenching mechanism governing PIN-TC interaction, while both PIN and PIN-TC complex exhibited excellent photo stability. Density functional theory calculations elucidated the molecular binding mechanism, showing strong agreement with experimental observations. Comprehensive biological evaluation using Epinephelus coioides eye muscle cells confirmed negligible cytotoxicity, while antimicrobial assessments against Klebsiella pneumoniae and Staphylococcus aureus demonstrated preserved antibiotic efficacy. Bio-imaging capabilities were successfully validated using Daphnia pulex as a model organism. The practical utility of PIN sensor was rigorously assessed across twelve diverse matrices including environmental waters, biological fluids, food beverages, and tissue samples, with recovery rates of 97.0-102.5 % validated against HPLC analysis. This work presents a versatile, cost-effective platform for TC monitoring in complex real-world samples.