Modulation of inner filter effect of non-conjugated silver nanoparticles on blue emitting ZnS quantum dots for the quantitation of betahistine.

A simple, reliable and efficient fluorescent probe has been developed for the detection and quantitation of betahistine using inner filter effect (IFE) of silver nanoparticles (AgNPs) on zinc sulphide (ZnS) quantum dots. The synthesized ZnS exhibited blue emission at 403 nm which was quenched upon mixing with AgNPs due to intensive localized surface plasmon resonance (LSPR) absorption at 401 nm. The presence of IFE was confirmed by UV-Visible and fluorescence spectroscopy, dynamic light scattering and transmission electron microscopy. Addition of betahistine caused aggregation of AgNPs as visualized by the change in colour of nano-suspension. The reduced absorption at LSPR resulted in inhibition of IFE leading to higher fluorescence intensities in the presence of betahistine. Parameters such as pH, incubation time and concentration of AgNPs were suitably optimized. The fluorescence signal (I - I0/I0) responded linearly for betahistine in the concentration range from 0.1 to 10 μM under the optimized experimental conditions. Due to the aggregation of AgNPs, a simple colorimetric approach was also studied for quantitation of betahistine in the range 1.0-20 μM. The limit of detection for fluorescence measurement and colorimetric approach was 0.02 μM and 0.23 μM, respectively. Further, the proposed method exhibited excellent selectivity towards betahistine in presence of several cations, biomolecules such as glucose, uric acid, creatinine, amino acids and several anti-vertigo medications. The method was applied to quantify betahistine from pharmaceutical products and results obtained were in good agreement with the claimed values. The proposed sensor can serve a low cost, selective, sensitive and a precise tool for routine quantitation of betahistine.