Manganese-Doped Carbon Dots for Sensitive Fluorescence Detection of Ciprofloxacin in Environmental and Pharmaceutical Samples

A simple and sensitive fluorescence sensing method was developed for ciprofloxacin (CIP) determination based on manganese-doped carbon dots (Mn-CDs). The Mn-CDs were synthesized through a one-step hydrothermal method using anhydrous citric acid and manganese chloride tetrahydrate as precursors. The prepared Mn-CDs exhibited good dispersibility, uniform nanoscale morphology, abundant surface functional groups and favorable fluorescence properties. The incorporation of Mn was designed to introduce coordination-related binding sites for CIP, thereby enhancing the interaction between Mn-CDs and CIP. Under excitation at 330 nm, the Mn-CDs showed a pronounced fluorescence enhancement response toward CIP, enabling their use as fluorescent probes for quantitative detection. Under the optimized conditions, the fluorescence intensity increased linearly with CIP concentration over the range of 20 nM–10 μM, with a detection limit of 1.12 nM. The proposed sensing system exhibited satisfactory selectivity toward CIP over various potentially interfering substances and good storage stability. The practicality of the method was further verified by analysis of pond water samples, affording recoveries of 86–118% with relative standard deviations below 5%. In addition, the method showed acceptable applicability for CIP determination in different pharmaceutical formulations. These results indicate that the Mn-CD-based fluorescent probe provides a convenient, sensitive and promising platform for CIP determination in environmental and pharmaceutical samples.