Fluorescent carbon nanoparticles as label-free recognizer of Hg2+ and Fe3+ through effective fluorescence quenching in aqueous media

Preparation, characterization and ion sensing property of water-dispersible fluorescent carbon nanoparticles (CNPs) is reported. These CNPs are prepared from inexpensive source (candle soot) with a water-based preparation without using organic solvent. Excitation-independent fluorescence behavior is a notable feature of these CNPs, which is found in limited reports in the literature. These CNPs exhibit selective dual metal ion (Hg2+ and Fe3+) recognition in aqueous media out of a large number of metal ions investigated. They also exhibit green fluorescence under UV light (365 nm) exposure, which disappears upon addition of Fe3+ and Hg2+. The fluorescence quenching due to the aggregation of CNPs in presence of Hg2+ and Fe3+ is supported by TEM and AFM studies. Detail studies on stability of CNPs, selectivity, interference, reversible binding of metal ion and optimum experimental conditions for sensing of metal ions were carried out. The detection limits for Hg2+ and Fe3+ (80 and 40 nM) and the linear range was 160-2000 nM.