Fluorescent aptasensor for ofloxacin detection based on the aggregation of gold nanoparticles and its effect on quenching the fluorescence of Rhodamine B.

This paper proposes the idea of building a fluorescent biosensor for ofloxacin (OFL) determination in aqueous and milk samples by label-free OFL-specific aptamer, gold nanoparticles (AuNPs) and Rhodamine B (RB). In the absence of OFL, AuNPs are coated with OFL aptamer and maintain dispersed in the high concentration of NaCl. The dispersed AuNPs could reduce the strong fluorescence intensity of RB efficiently. By contrast, in the presence of OFL, OFL is combined with aptamer to form stable compounds, causing the aptamers separated from the surface of AuNPs, thus AuNPs would be exposed in the solution. And the aggregated AuNPs will not quench the fluorescence intensity of RB. Through the distinction of the fluorescence intensity, the concentration of OFL could be detected in aqueous and milk samples quantitatively. The convenient and specific fluorescent assay for OFL is established with a linear range (R = 0.9907) from 20 to 300 nM and a detection limit of 1.66 nM in aqueous solution, and a linear range (R = 0.9963) from 20 to 300 nM and a detection limit of 4.61 nM (1.66 μg/L) in milk samples. With the good sensitivity and selectivity, this biosensor has good application potential to detect OFL in food and environmental samples.