CeFe nanofibrous carbon nanozyme integrated with smartphone for the point-of-care testing of norfloxacin in water

The overuse of antibiotics has led to the severe contamination of water bodies, posing a considerable hazard to human health. Therefore, the development of an accurate and rapid point-of-care testing (POCT) platform for the quantitative detection of antibiotics is necessary. In this study, Cerium oxide (CeO₂) and Ferrosoferric oxide (Fe₃O₄) nanoparticles were simultaneously encapsulated into N-doped nanofibrous carbon microspheres to form of a novel nanozyme (CeFe-NCMzyme) with a porous structure, high surface area, and N-doped carbon material properties, leading to a considerable enhancement of the peroxidase (POD)-like activity compared with that of the CeO₂ or Fe₃O₄ nanoparticles alone. The POD-like activity of CeFe-NCMzyme can be quenched using L-Cysteine (Cys) and subsequently restored by the addition of a quinolone antibiotic (norfloxacin, NOR). Therefore, CeFe-NCMzyme was used as a colorimetric sensor to detect NOR via an “On-Off” model of POD-like activity. The sensor possessed a wide linear range of 0.05-20.0 μM (R² = 0.9910) with a detection limit of 35.70 nM. Furthermore, a smartphone-assisted POCT platform with CeFe-NCMzyme was fabricated for quantitative detection of NOR based on RGB analysis. With the use of the POCT platform, a linear range of 0.1-20.0 μM and a detection limit of 54.10 nM were obtained. The spiked recoveries in the water samples were ranged from 97.73% to 102.01%, and the sensor exhibited good accuracy and acceptable reliability. This study provides a portable POCT platform for the on-site and quantitative monitoring of quinolone antibiotics in real samples, particularly in resource-constrained settings.