A method is described for rapid (1 h) synthesis of gold nanoclusters (AuNCs) co-functionalized with serine and 11-mercaptoundecanoic acid. The co-functionalized AuNCs exhibit good stability towards temperature, pH values, and over time. They were characterized by atomic force microscopy, high-resolution transmission electron microscopy, dynamic light scattering, and by fluorescence, IR and X-ray photoelectron spectroscopies. The fluorescence of the AuNCs is quenched by Hg(II) and restored on subsequent addition of aureomycin (CTC) or oxytetracycline (OTC). A fluorescent turn-on assay was worked out for simultaneous detection of CTC and OTC based on recording the change of the restored fluorescence measured at 420 and 500 nm under 340 nm photoexcitation. The detection limits are 20 and 9 nM for CTC and OTC, respectively. The concentrations of CTC and OTC can also be visualized by UV illumination. The nanoprobe was successfully applied to the simultaneous determination of CTC and OTC in spiked human urine. Graphical abstract Schematic of a two-wavelength fluorescence recovery method for the simultaneous determination of aureomycin and oxytetracycline. It is based on the use of gold nanocrystals modified with serine and 11-mercaptoundecanoic acid, and on recording the change of the restored fluorescence measured at 420 and 500 nm.
Keywords: Antibiotics; Fluorescence; Gold nanoclusters; Quenching; Visual detection.