Enhanced emission and higher stability ovalbumin-stabilized gold nanoclusters (OVA-AuNCs) modified by polyethyleneimine for the fluorescence detection of tetracyclines

Tetracyclines, cheap and broad-spectrum antibiotics, are required to strictly monitor since they can lead to ecosystem disorders and the flood of resistance genes if overused. Although ovalbumin has been reported to synthesize metal nanoclusters for fluorescence detection, relatively low fluorescence intensity and quantum yield limited their application. In this study, ovalbumin-stabilized gold nanoclusters (OVA-AuNCs) modified by polyethyleneimine (PEI-OVA-AuNCs) with higher fluorescence intensity and quantum yield were successfully synthesized and applied to develop a sensitive fluorescent detection method for tetracycline antibiotics. The fluorescence intensity of the stable PEI-OVA-AuNCs modified with 10 μM PEI was 8.5 times stronger than unmodified OVA-AuNCs. The reason of the fluorescence intensity enhancement could be attributed to etching OVA-AuNCs from large particles to smaller ones by PEI and formation of a protective layer on the outside of the clusters to avoid non-radiative relaxation. The fluorescence quenching was linearly related to tetracycline (TC) in the concentration range 1–30 μM, and the detection limit was 0.563 μM. Meanwhile, the fluorescent probe could detect oxytetracycline and chlortetracycline with the linear correlations higher than 0.99. The quenching mechanism was inner filter effect caused by the overlap of the spectra of PEI-OVA-AuNCs and pollutants, and the aggregation-induced quenching caused by the binding of phenolic hydroxyl and ketone carbonyl groups on the pollutants to the probe as well. The method was successfully applied to the determination of TC in real samples. Therefore, PEI-OVA-AuNCs could be considered as a core material for tetracyclines fluorescence detection.