Dual-mode sensing by cobalt oxyhydroxide nanosheets for antibiotics

Abstract

Here, we present a cobalt oxyhydroxide (CoOOH) nanosheet-driven dual-mode sensor for fluoroquinolone antibiotic detection using fluorescence and colorimetric strategies. By using the intrinsic oxidizing ability of CoOOH nanosheets, 3,3′,5,5′-tetramethylbenzidine (TMB) was directly oxidized, resulting in its blue product (oxTMB), enabling sensitive and selective detection. A fluorescence quenching effect was observed owing to the inner filter effects (IFEs), showing a noticeable change in the blue coloration through interaction with fluoroquinolones (ofloxacin, norfloxacin, and ciprofloxacin). The system exhibited excellent sensitivity with linear responses in the range of 0–250 nM with the lowest detection limits of 2.23 nM, 19.31 nM, and 29.03 nM for ofloxacin, norfloxacin, and ciprofloxacin, respectively, outperforming many existing sensors. These findings provide a novel scheme for the fluorescence and colorimetric analysis of antibiotics in water. Furthermore, a cost-effective, mobile-device-assisted paper-based sensing system was developed for the quick and visual field-level detection of fluoroquinolones. These sensors provide a practical and user-friendly tool for rapid antibiotic screening, which can be completed within minutes. The proposed system offers a promising strategy for environmental and pharmaceutical monitoring, using CoOOH nanosheets as versatile components for sensor development.