Chelation enhanced fluorescence of rhodamine based novel organic nanoparticles for selective detection of mercury ions in aqueous medium and intracellular cell imaging.

• Fluorescent organic nanoparticles FONs-RSB prepared by reprecipitation method. • FONs-RSB showed Chelation enhanced fluorescence only in the presence of Hg2+. • Interference-free detection of Hg2+ ions using a proposed sensing method. • The extremely low detection limit of 1.729 ng/mL for Hg2+ ions in an aqueous medium. • Feasibilities are analysis of environmental samples and intracellular cell imaging. A simple, quick and useful reprecipitation method was used to prepare rhodamine based fluorescent nanoparticles. The characterization techniques such as zeta-particle sizer and scanning electron microscopy were studied to investigate the formation of desired nanoparticles FONs-RSB along with its aqueous stability, surface charge, particle size, and morphological features. The comparative optical properties between parent molecule RSB and FONs-RSB were examined using absorption and fluorescence studies. The sphere morphology of FONs-RSB having 82 nm particle size and negative zeta potential (−33.5 mV) showed selective and sensitive interaction with only Hg2+ amongst the series of metal ion studied which was revealed by florescence titration results. The interaction between FONs-RSB and Hg2+ leads to enhance the fluorescence of FONs-RSB is because of chelation enhanced fluorescence (CHEF) phenomenon. The interference of foreign metal ions was found to be unaffected to the fluorescence enhancement induced by Hg2+. The binding stoichiometry and binding constant were evaluated using Job's and modified Benesi-Hildebrand plot. The mechanism of binding interaction and nature of complexation were analyzed using Infrared (IR), Nuclear Magnetic Resonance (NMR), absorption and fluorescence lifetime titrations in the absence and presence of a variable amount of Hg2+ to FONs-RSB. Further, the reaction product of the sensing process in the present investigation was examined using mass analysis. The detection limits calculated using the present method were found to be 1.729 ng/mL (8.619 nM) and 1.68 ng/mL when linear concentration of Hg2+ additions were 0−2 μg/mL and 0−100 ng/mL, respectively. The practical application of the present method involves the quantitative determination of Hg2+ in environmental samples collected from the local campus and intracellular cell imaging of Hg2+ using A375 living cells with non-toxic behavior. [ABSTRACT FROM AUTHOR]