A novel enzymatic biosensor for CIP in food based on UCNPs and colorimetric strategy of potassium titanium oxalate

A novel enzymatic biosensor was developed for the determination of ciprofloxacin (CIP) using upconversion nanoparticles (UCNPs) and the color development strategy of potassium titanium oxalate (PTO). The presence of CIP triggers the specific recognition of CIP by the aptamer, which leads to the dissociation of PDA-encapsulated magnetic nanoparticles (Fe 3 O 4 @PDA-Apt) from the horseradish peroxidase-functionalized UCNPs (cDNA-UCNPs-HOR) and facilitates fluorescence recovery. Accordingly, CIP demonstrated the ability to indirectly alter the quantity of H 2 O 2 , where PTO could selectively interact with H 2 O 2 , leading to the formation of yellow peroxo-titanic acid, which enabled the colorimetric detection of CIP. Under ideal conditions, the linear ranges for fluorescence and colorimetry were 10–1000 µg L −1 and 100–1000 µg L −1 , respectively, with detection limits (LOD) of 2.1 and 16.7 µg L −1 . Finally, the precision and accuracy of the method were validated with HPLC and achieved satisfactory results ( P  > 0.05).