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Graphical representation of the binding of CURNPs to Cu2+(fluorescence off) and release of CURNPs (fluorescence on) by the reaction of S2−with copper bound to CURNPs.

CTAB-PNPs are bound to dichromate ion by electrostatic interaction to form stable non-fluorescent micellar complex which is responsible for the ‘FL quenching’ of CTAB-PNPs.

The hydrophobic force of interaction between R6G and SDS stabilized PyNPs involving FRET was demonstrated by measuring fluorescence of nanoparticles as a function of concentration of R6G.

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Fluorescent perylene nanoparticles were prepared by a reprecipitation method in the presence of cetyltrimethylammonium bromide (CTAB) as a stabilizer. The formation of perylene nanoparticles was confirmed by dynamic light scattering , UV-visible absorption spectroscopy, fluorescence spectroscopy and excited state life time measurements. The observation of a significant large Stoke's shift (24 546 cm À1 ) of perylene nanoparticles in aqueous suspension as compared with that of a dilute solution of perylene in acetone (14 250 cm À1 ) indicated aggregation of molecules in their ground state by lateral p-stacking. A highly intense, single band fluorescence peak at 565 nm is attributed to the direct excitation of perylene nanoparticles (l ex ¼ 380 nm) due to aggregation induced enhanced emission (AIEE) and is quenched appreciably by HCO 3 À anions. A positive surface charge is created by the CTAB cage on the nanoparticles and binding interactions result in quenching of fluorescence of perylene nanoparticles which is observed in the spectrum at 565 nm. The quenching of perylene nanoparticles emission is linear in the concentration range of 0-80 mM of HCO 3 À ion in solution. The quenching results obey the Stern-Volmer relation and the method after calibration can be applied successfully in the quantitative analysis of sodium bicarbonate in commercially available medicinal tablets.

The nanoparticles of highly fluorescent Rubrene prepared by reprecipitation method using Sodium Dodecyl Sulphate (SDS) exhibited narrower particle size distribution when examined by Dynamic Light Scattering (DLS) technique. The average particle size obtained is 87.2 nm and zeta potential -13.8 mV given by zeta sizer indicated that the Rubrene Nanoparticles (RUBNPs) entrapped in SDS surfactant has charged negatively by which it can change the photo absorption and emission properties of aqueous suspension of nanoparticles. The red shifted UV -photo absorption band of RUBNPs in comparison with absorption band of rubrene in Tetrahydrofuran (THF) solution is because of J-type aggregates in aqueous suspension of nanoparticles, which also results into Aggregation Induced Enhanced Emission (AIEE) at λmax = 564 nm. The presence of Fe 2+ in the aqueous suspension of RUBNPs showed quenching of fluorescence at 564 nm and quenching results fits into conventional Stern-Volmer relation in the concentration range of 0-80 μg/mL of Fe 2+ ion solution with good linear relationship. The possible mechanism of fluorescence quenching of RUBNPs is explained by considering adsorption of Fe 2+ cation electrostatistically on the negatively charged surface of the nanoparticle generated by SDS capping. The proposed sensing method ofRUBNPsto selective detection of Fe 2+ ion is successfully applied for quantification of Fe 2+ from pharmaceutical tablet.