Surface-enhanced raman scattering using fluorescence-quenched carbon quantum dots for mercury ion detection

Mercury ion (Hg2+) is one of the most challenging problems due to its high toxicity at low concentration and bioaccumulative effects affecting human health. Herein, we propose a strategy to exploit the fluorescence quenching of carbon quantum dots (CQDs) combined with surface-enhanced Raman scattering (SERS) technique to detect Hg2+. CQDs exhibit strong fluorescence emission interfering SERS measurement. However, with the presence of Hg2+, fluorescence from CQDs can be quenched, and the SERS spectrum can be collected. In this work, SERS spectra of rhodamine 6G (R6G) incorporated with CQDs and Hg2+ (0.100‒100 ng/L) were studied. The SERS spectra of R6G was used as an indicator for Hg2+ concentration. Upon the addition of Hg2+, the SERS spectra of R6G showed changes in the intensity. To quantify Hg2+, the Raman intensity of R6G at 615 cm-1 (I615) was linearly plotted against the concentrations of Hg2+ with R2 = 0.963 in the range of  0.100–0.800 ng/L. The limit of detection (LOD) of Hg2+ is 0.190 ng/L. Also, the selectivity was conducted by using various metal ions as interfering ion. The developed technique shows good selectivity to detect Hg2+. This technique can be used for a practical application in a real water sample. The mineral drinking water sample was used as practical application with LOD of Hg2+ is 0.194 ng/L and R2 = 0.935, ranging from  0.100–0.800 ng/L. Our developed technique was validated using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). This developed SERS technique provides a simple sample pretreatment, sensitivity, and good selectivity.