Dual fluorescence-colorimetric sensor based on silver nanoparticles for determination of tobramycin in its pharmaceutical preparations

The purpose of this study is to develop a dual fluorescence-colorimetric sensor for determination of the non-chromophoric drug, tobramycin using fluorescein-modified silver nanoparticles. Fluorescein is adsorbed on the surface of silver nanoparticles resulting in quenching of the fluorescence intensity of fluorescein at 513 nm. Upon addition of tobramycin to fluorescein-bound silver nanoparticles, tobramycin can displace fluorescein from the surface of nanoparticles resulting in nanoparticles aggregation and liberation of free fluorescein restoring its fluorescence. The interaction of tobramycin with fluorescein-bound silver nanoparticles is manifested by a decrease in the surface plasmon resonance band of silver nanoparticles at 395 nm, an increase in the fluorescence intensity of fluorescein at 513 nm and color change of the colloidal solution from yellow to light pink. These spectral effects are directly proportional to the concentration of tobramycin with a linearity range of 0.10 – 0.45 μg mL-1 and 0.05 – 0.45 μg mL-1 for the spectrophotometric and spectrofluorimetric methods, respectively. The proposed methods were applied for determination of tobramycin in Tobrin® ophthalmic solution with mean %recovery ± standard deviation of 99.036 ± 1.737 for the spectrophotometric method and 101.192 ± 1.315 for the spectrofluorimetric method. The optical sensor is simple, rapid, and cost-effective and can be used for determination of tobramycin in bulk and in its pharmaceutical preparations.