Carbon dots as nanosensor for sensitive and selective detection of Hg2+ and L-cysteine by means of fluorescence Off-On switching

An Off-On approach for highly sensitive and selective detection of mercury ions (Hg2+) and L-cysteine (L-Cys) was demonstrated with the use of water-soluble carbon dots (CDs) as novel fluorescent probe. In this present sensing system, Hg2+ cations can efficiently coordinate onto the surface of CDs by means of electrostatic interactions and remarkably quench the fluorescence signal of CDs as a result of the fluorescence charge transfer (turn-off). In addition, the resulting CD5-Hg2+ system was observed to be sensitive to L-Cys due to the ability of L-Cys to coordinate with Hg2' and the formation of strong Hg2*-SR bond. When L-Cys was added, Hg2+ combined with L-Cys rather than with CDs resulting in the remove of Hg2+ from the surface of CDs and shielding of fluorescence quenching, and thus, a significant fluorescence restore of CDs was observed (turn-on). Under the optimized conditions, good linearity for detecting Hg2' was attained over the concentration range from 2 to 22 mu M with a detection limit of 0.017 mu M, while the concentrations of L-Cys ranging from 2 to 20 mu M exhibited a linear relationship with the relative fluorescence intensity with a correlation coefficient of R-2 = 0.99329. Moreover, this CDs-based sensor was successfully applied for visual identification and quantitation of Hg2+ and L-Cys in real water sample and fluorescence imaging of NIH-3T3 cells with satisfying resolution. (C) 2015 Elsevier B.V. All rights reserved.