Dithioerythritol-capped silver/gold nanoclusters for determination of ciprofloxacin, norfloxacin, and enrofloxacin in food and urine samples

Abstract

Fluoroquinolones (FQs) are widely used in the poultry and livestock industries due to their effectiveness in preventing and treating bacterial infections. However, improper use and poor biodegradability lead to their accumulation in the food chain, posing risks to human health. To address this, a novel ratiometric fluorescence probe was developed for sensitive FQ detection. The probe consists of dithioerythritol-protected silver–gold nanoclusters (DIT@AgAuNCs) with weak red fluorescence at 615 nm. Addition of Al³⁺ induces nanocluster aggregation, enhancing fluorescence emission. Upon adding FQs to the DIT@AgAuNCs/Al³⁺ system, fluorescence at 615 nm decreases due to the removal of Al³⁺ from the ligand (DIT) surface via coordination interactions. Simultaneously, a new blue fluorescence peak emerges at 465 nm, attributed to the formation of an Al³⁺-FQs coordination complex. Under optimal conditions, the fluorescence ratio (F₄₆₅/F₆₁₅) increased proportionally with FQ concentration. In this study, F₄₆₅/F₆₁₅ represents the ratio of fluorescence intensity at 465 nm (blue emission from the Al³⁺-FQ complex) to that at 615 nm (red emission from aggregated DIT@AgAuNCs). This ratiometric approach compensates for environmental and instrumental fluctuations, enhancing analytical reliability. The probe exhibited good linearity for ciprofloxacin (CIP), norfloxacin (NOR), and enrofloxacin (ENR) within the ranges of 0.01–60 μM, 0.018–60 μM, and 0.021–60 μM, respectively, with detection limits 0° 31 nM, 38 nM, and 44 nM. The probe was successfully applied to detect FQs (using CIP as an example) in egg, milk, and urine samples, demonstrating high accuracy with recoveries of 94.0–106.0% and excellent reliability, with an RSD below 4.09%.