A highly selective “turn-on-off” fluorescent probe utilizing N, S co-doped carbon quantum dots for the determination of moxifloxacin and ofloxacin in honey

Fluorescent analysis technology has received widespread recognition in the field of rapid detection due to its simplicity, high sensitivity, and selectivity. Carbon quantum dots possess abundant surface groups, excellent biocompatibility, and fluorescence stability, making them outstanding fluorescent probes for the detection of antibiotics. In this study, a highly selective “turn-on-off” fluorescent probe utilizing nitrogen and sulfur co-doped carbon quantum dots (N, S-CQDs) for the on-site detection of moxifloxacin (MXF) and ofloxacin (OFX) in honey was fabricated. Due to the aggregation-induced emission effect, the fluorescence of the probe at 515 nm was significantly increased through hydrogen bond or π-π interactions with MXF and OFX. The subsequent addition of Cu²⁺ led to the formation of a non-fluorescent N, S-CQDs-MXF-Cu²⁺ or N, S-CQDs-OFX-Cu²⁺ ternary complex, resulting in static fluorescence quenching. Strong linear correlations were observed between the Cu²⁺-induced relative fluorescence quenching efficiency (ΔF/F₀) and antibiotic concentrations (0.02–8 mg·L⁻¹ for MXF and 0.1–20 mg·L⁻¹ for OFX). The developed assay demonstrated high specificity and sensitivity, with LOQs ranging from 9.3 to 9.6 μg∙L⁻¹. Moreover, MXF, OFX and their mixtures can be effectively distinguished using linear discriminant analysis. The fluorescent probe was successfully applied to a test strip, which enables the detection of MXF and OFX in honey with the aid of a smartphone.