Novel metal nanoparticle-enhanced fluorescence for determination of trace amounts of fluoroquinolone in aqueous solutions

Metal-enhanced fluorescence of fluoroquinolones (FQs) was first observed in aqueous solutions. In addition, a new type of silver nanoparticles (AgNP) was synthesized with simple and easy synthetic processes and environmentally friendly compounds. The effects of different concentrations of AgNPs on the fluorescence behaviours of ciprofloxacin (CIP), enrofloxacin (ENR) and lomefloxacin (LMF) in aqueous solutions were investigated, respectively. The experimental results demonstrated that the fluorescence peak shapes and the locations of the features in the excitation and emission spectra for each FQ that was mixed with AgNPs were almost the same as those of the standard FQs. An enhancement or quenching of the fluorescence can also be observed, depending on the exact conditions. Compared with the identical control samples that lack AgNPs, the fluorescence of each FQ in aqueous solutions was greatly enhanced by AgNPs with concentrations at a volume ratio of 5%. Moreover, at the optimum AgNP concentration, novel sensitive fluorometric methods for the separate determination of trace amounts of CIP, ENR and LMF in aqueous solutions were established. Under optimal experimental conditions, the linear dynamic ranges for the determination of CIP, ENR and LMF concentrations varied from 0.025 to 1.0 mg L-1, 5.0 to 160 ng L-1 and 0.01 to 0.8 mg L-1, and the limits of detection were 90, 5 and 6 ng L-1, respectively; the relative standard deviation was less than 1.2% (n = 9). The experimental recovery results for the determination of CIP, ENR and LMF in aqueous solutions ranged from 99% to 102%, 90% to 103% and 92% to 107%, respectively. Compared with the established method in which no AgNPs were added, the quantitation limits of the silver nanoparticle-enhanced fluorometric methods were approximately 2-fold lower for CIP, 2.6-fold lower for ENR and 4-fold lower for LMF. Significantly, the novel silver nanoparticle-enhanced fluorometric methods were successfully applied to directly determine CIP, ENR and LMF concentrations in pharmaceutical preparations, demonstrating the methods' advantages of simplicity, sensitivity and low cost.