Carbon dot nanosensors for ultra-low level, rapid assay of mercury ions synthesized from an aquatic weed, Typha angustata Bory (Patera)

Abstract

A wild plant, Typha angustata Bory (Patera) was used as a precursor for synthesizing nitrogen and sulfur doped carbon dots (N, S-CDs) using hydrothermal method. The objective was to use an aquatic weed to develop an extremely sensitive sensor for fluorescence assay of mercury ions and cysteine in aqueous medium. N, S-CDs exhibited an unprecedented quantum yield (QY) of 83 %, not reported previously. The fluorescence intensity of N, S-CDs substantially quenched in presence of Hg 2+ ions, without being influenced with presence of interfering ions. The fluorescence intensity was regained absolutely in presence of cysteine, even after 10 cycles demonstrating exceptional reusability. Owing to extraordinary QY, the sensor exhibited ultra-low limits of detection (LOD) of 3.1 nM and 80 pM for Hg 2+ and cysteine, respectively indicating extraordinary efficacy of the sensor, also confirmed using XPS studies. At neutral pH and 2 min' incubation time, the linear detection ranges for Hg 2+ ions and cysteine were 0.01–60 μM and 0.05–12.5 μM, respectively. Fluorescence life decay studies exhibited that fluorescence quenching was static. Satisfactory recoverability in the range 95–102 % for real water samples, indicated high reliability and accuracy for detection of Hg 2+ ions. The synthesized sensor presented a potential for facile, fast and reliable platform for detection of Hg 2+ ions and cysteine for environmental remediation. • Wild plant, Typha angustata Bory was used as a precursor for N and S doped carbon dots. • The sensor exhibited “on-off” and “off-on” fluorescence sensing of mercury ions and cysteine. • Exceptionally low LOD of 3.1 nM and 0.08 nM were obtained for Hg 2+ and cysteine. • Excellent reversibility of fluorescence signal with cysteine was obtained for 10 cycles.