Simultaneous detection of tetracyclines and ofloxacin via carbon dots based ratiometric fluorescence and portable hydrogel-based visual detection of ofloxacin.

Determination of antibiotic residues is vital to food safety because of their potential bioaccumulation through the food chain. Herein, orange-red carbon dots (O-CDs) were fabricated by optimizing reaction conditions for fluorometric sensing of tetracyclines (TCs) and ofloxacin (OFx). Upon 375 nm excitation, the O-CDs exhibit dual emission peaks at 400 nm and 530 nm. TCs quench both emissions, while OFx quenches the emission at 400 nm but enhances that at 530 nm. Self-calibrated ratiometric sensing (F400/F530) enabled simultaneous discrimination of TCs and OFx, achieving low detection limits (0.17-0.49 μM) with recoveries of 88.34-103.50% and relative standard deviations (RSDs) of 0.95-5.51% in real samples. Furthermore, a portable hydrogel-based colorimetric sensor for OFx was developed, enabling rapid visual detection via a smartphone over a 1-1000 μM range, with a detection limit of 0.98 μM, recoveries of 99.33-103.60%, and RSDs of 1.50-3.42%, offering a promising strategy for antibiotic monitoring and food-safety applications.