A rapid and label-free dual detection of Hg (II) and cysteine with the use of fluorescence switching of graphene quantum dots
Sensors and Actuators B: Chemical, 207, pp 490-497, 2015-2
A simple and rapid method of analysis for mercury ions (Hg2+) and cysteine (Cys) was developed withthe use of graphene quantum dots (GQDs) as a fluorescent probe. In the presence of GQDs, Hg2+ cations are absorbed on their negatively charged surface by means of electrostatic interactions. Thus, the fluorescence (FL) of the GQDs would be significantly quenched as a result of the FL charge transfer, e.g. 92% quenching at 450 nm occurs for a 5 mu mol L-1 Hg2+ solution. However, when Cys was added, a significant FL enhancement was observed (510% at 450 nm for a 8.0 mu mol L-1 Cys solution), and Hg2+ combined with Cys rather than with the GQDs in an aqueous solution. This occurred because a strong metal thiol bond formed, displacing the weak electrostatic interactions, and this resulted in an FL enhancement of the GQDs. The limits of detection (LOD) for Hg2+ and Cys were 0.439 nmol L-1 and 4.5 nmol L-1, respectively. Also, this method was used successfully to analyze Hg2+ and Cys in spiked water samples.
Graphene quantum dots; Citric acid; Mercury (II) ions; Cysteine; Fluorescence switching