A ratiometric fluorescence and smartphone-assisted dual-mode sensing platform based on dual-emissive carbon quantum dots for highly sensitive and visual monitoring of ciprofloxacin in food samples.

The abuse of ciprofloxacin (CIP) in animal husbandry poses a threat to public health. In this study, a novel dual-mode sensing platform based on dual-emissive carbon quantum dots (DE-CQDs) combining ratiometric fluorescence and smartphone-assisted visualization was developed for the first time for rapid, ultra-sensitive, low-cost and on-site visual quantification of CIP. DE-CQDs were synthesized via a facile one-pot hydrothermal treatment of cinnamic acid and o-phenylenediamine. The introduction of CIP selectively enhanced the fluorescence intensity at 453 nm, whereas the emission at 560 nm remained constant, causing an apparent color transition from yellow to blue. The sensor achieves a CIP detection limit of 13.5 nM (ratiometric fluorescence) and 65.2 nM (smartphone-assisted). It was successfully utilized for CIP detection in milk and meat samples with high accuracy. This sensor outperforms the traditional dual-material sensors in terms of synthesis simplicity, low cost and good stability, offering a promising strategy for food safety monitoring.