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 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.

Fluorescent Tetracene Nanoparticles (TNPs) have been prepared by a reprecipitation method using cetyl trimethyl ammonium bromide (CTAB) as a stabilizer. These TNPs are more photostable against photobleaching and high solubility in water minimize the utilization of hazardous organic solvents compared with single organic fluorophore in sensing applications. The method based on fluorescence quenching TNPs as a novel fluorescent sensor for selective recognition of fast green FCF dye in aqueous solution. The fluorescence intensity of TNPs was quenched by the successive addition on increasing concentrations of fast green FCF dye. The fluorescence quenching results were found to fit the Stern-Volmer (S-V) relationship in the range of 0.5-7.0 µg L -1 with a correlation coefficient of 0.999. The limit of detection (LOD) was 0.136 µg L -1 . Moreover, the excited state lifetime of TNPs remains unchanged even after increasing concentration fast green FCF dye suggest that fast green FCF dye adsorbed over the surface of the nanoparticles to form non-fluorescent ground state complex i.e. nature of quenching process is static. The proposed method was successfully applied for the quantitative analysis of fast green FCF dye in commercial samples with no necessity of prior separation of analyte molecules form the interfering constituents.

The aqueous suspension of fluorescent nanoparticles were prepared by using 9-anthradehdye derivative (AH). The nanoparticles (AHNPs) were characterized using DLS-zeta sizer and SEM techniques. The photo physical properties of nanoparticles and precursor were measured and compared using UV-absorption spectroscopy, fluorescence spectroscopy and fluorescence lifetime studies. The significant overlap between fluorescence spectrum of AHNPs and excitation spectrum of Riboflavin (RF) led us to explore Fluorescence Resonance Energy Transfer (FRET) studies between AHNPs and RF in aqueous medium. The mechanism of FRET from AHNPs to RF discussed on spectral observations, thermodynamic parameters and changes produces in fluorescence lifetime in absence and presence of different concentrations of RF to AHNPs. The limit of detection for RF (0.071 µM) is considerably low compared with reported methods. Thus, we explore AHNPs as novel nano probe for quantitative determination of RF in pharmaceutical samples based on FRET study. In addition with this, AHNPs has excellent antibacterial activity than the bulk material for two different bacteria culture viz. E. coli and Bacillus sps. Graphical Abstract 9-anthradehdye based fluorescent nanoparticles (AHNPs) explores as nano probe to detect Riboflavin (RF) in aqueous medium based on Fluorescence Resonance Energy Transfer (FRET) studies. The proposed analytical method successfully applied for quantitative determination of RF in pharmaceutical samples. In addition, with this, AHNPs has excellent antibacterial activity than the bulk material for two different bacteria culture suspension viz. E. coli and Bacillus sps.

A simple solid state reaction technique was employed for the preparation of polycrystalline luminophors of p-terphenyl containing different amounts of perylene followed by spectral characterization techniques viz. XRD, SEM, TGA-DSC, UV-Visible spectroscopy, thermo-electrical conductivity, fluorescence spectroscopy, fluorescence life time spectroscopy and temperature dependent fluorescence. X-ray diffraction profiles of the doped p-terphenyl reveal well-defined and sharp peaks indicate homogeneity and crystallinity. The SEM micrograph of pure p-terphenyl exhibit flakes like grains and then compact and finally gets separately with perylene amounts. The observed results indicate that closed packed crystal structures of doped p-terphenyl during crystal formation. The band gaps estimated from UV-visible spectroscopy decreased from 5.20 to 4.10 eV, while thermo-electrical conductivity increases with perylene content. The fluorescence spectra showed partial quenching of p-terphenyl fluorescence and simultaneously sensitization of perylene fluorescence at the excitation wavelength of p-terphenyl (290 nm) due to excitation energy transfer from p-terphenyl to perylene. The observed sensitization results are in harmony with intense blue color seen in fluorescence microscopy images and has high demand in scintillation process.