A CQDs-doped europium-DPA framework for fluorescence and colorimetric dual-mode sensing of amoxicillin and ciprofloxacin.

Amoxicillin (AMO), a penicillin antibiotic, and ciprofloxacin (CIP), a quinolone antibiotic, are widely used to combat bacterial infections and are frequently co-administered to enhance therapeutic efficacy. However, improper use of AMO and CIP may lead to antibiotic residues in the environment, posing serious threats to human health. The visual detection of AMO and CIP remains significant challenges. Herein, the Eu-DPA@CQDs was used for the dual-mode detection of AMO and CIP, which was synthesized by CQDs doped in europium-DPA metal-organic framework. In the colorimetric mode, the catalase-mimicking Eu-DPA@CQDs oxidized TMB to blue oxTMB. Upon addition of AMO, the oxTMB was reduced, causing color fading. Subsequent introduction of CIP restored nanozyme activity, regenerating the blue signal and enabling dual-analyte antibiotic detection. In the fluorescence mode, the Eu-DPA@CQDs probe exhibited dual emission at 440 nm and 613 nm. Upon AMO addition, the fluorescence at both wavelengths was quenched, accompanied by a color change from red to purple. In the presence of CIP, the emission at 440 nm increased and redshifted to 490 nm, while the signal at 613 nm was quenched, resulting in a multicolor transition from red to cyan. The Eu-DPA@CQDs sensor enabled rapid and dual-mode detection of AMO and CIP. The colorimetric method exhibited wide linear ranges of 0.005-25 μM for AMO and 0.007-4.25 μM for CIP, with detection limits of 1.67 nM and 3.75 nM, respectively. A visible color transition from dark blue to colorless was observed with increasing AMO concentration, while the addition of CIP reversed the signal back to dark blue. Similarly, the fluorescence detection achieved wide linear ranges from 0.005 to 30 μM for AMO and 0.005 to 15 μM for CIP, with detection limits as low as 4.74 nM and 3.11 nM, respectively, also within only 1 min. As the concentration of AMO increased, the color shifted from red to purple. In contrast, increasing CIP concentration induced a color transition from red to cyan. These color transitions were both clearly visible to the naked eye. The sensor demonstrated excellent selectivity and anti-interference capability, providing a reliable platform for accurate, sensitive, and quantitative determination of both antibiotics in real samples.