Biomolecule-Assisted Synthesis of Blue-Emissive Gold Nanoclusters for Sensitive Analysis of Tetracycline Residues in Food and Feed

Tetracycline antibiotics (TCs), which are frequently used in animal production, may remain in food products and thus require reliable analytical monitoring. In this study, we developed a fluorescence-based method for detecting three kinds of TCs in animal-derived foods and feed, including tetracycline hydrochloride (TC), chlortetracycline hydrochloride (CTC), and oxytetracycline (OTC). l-proline (Pro) served as a reducing and stabilizing ligand, and sodium alginate (SA) functioned as a costabilizer and surface-passivating biomolecule. By providing a biomolecularly coordinated interface that may be associated with restriction of intramolecular motion, these components enabled the one-pot synthesis of water-soluble blue-fluorescent gold nanoclusters (Pro-SA-AuNCs). Compared with systems using Pro alone, the synergistic stabilization of Pro and SA enhanced the fluorescence intensity and stability of the resulting NCs. The resulting probes allowed the detection of TCs through inner filter effect (IFE) and aggregation-induced quenching (static quenching). These dual quenching pathways and their combination with economical and easily operable solid-phase extraction for sample pretreatment contributed to the observed relatively high sensitivity and wide linear response range (5-800 μM). The obtained limits of detections (0.16-0.54 μM) are comparable to reported probes (Table 1). Application to representative real samples, including milk, honey, and animal feed, yielded high recovery rates, which supports the method's applicability to complex samples. These results suggest that Pro-SA-AuNCs and related methods provide a feasible platform for the development of fluorescence-based detection formats for TCs.