Selective sensing of Fe2+ ions in aqueous solution based on fluorescence quenching of SDS capped rubrene nanoparticles: application in pharmaceutical formulation

The nanoparticles of highly fluorescent rubrene prepared by reprecipitation method using sodium dodecyl sulphate (SDS) exhibited narrower particle size distribution when examined by the Dynamic Light Scattering (DLS) technique. The average particle size obtained is 87.2 nm and the zeta potential -13.8 mV given by a zetasizer indicated that the rubrene nanoparticles (RUBNPs) entrapped in SDS surfactant are negatively charged therefore changing the photo absorption and emission properties of the aqueous suspension of nanoparticles. The red shifted UV-photo absorption band of RUBNPs in comparison with the absorption band of rubrene in tetrahydrofuran (THF) solution is because of J-type aggregates in the aqueous suspension of nanoparticles, which also results in Aggregation Induced Enhanced Emission (AIEE) at lambda(max) = 564 nm. The presence of Fe2+ in the aqueous suspension of RUBNPs showed quenching of fluorescence at 564 nm and the quenching results fit into a conventional Stern-Volmer relation in the concentration range of 0-80 mu g mL(-1) of Fe2+ ions solution with a good linear relationship. The possible mechanism of fluorescence quenching of RUBNPs is explained by considering the adsorption of the Fe2+ cation electrostatically on the negatively charged surface of the nanoparticle generated by SDS capping. The proposed sensing method of RUBNPs for selective detection of Fe2+ ion is successfully applied for the quantification of Fe2+ from pharmaceutical tablets.