Highly Selective and Sensitive Detection of Hg2+ Based on Förster Resonance Energy Transfer between CdSe Quantum Dots and g-C3N4 Nanosheets

In the presence of Hg 2+ , a fluorescence resonance energy transfer (FRET) system was constructed between CdSe quantum dots (QDs) (donor) and g-C 3 N 4 (receptors). Nanocomposites of g-C 3 N 4 supported by CdSe QDs (CdSe QDs/g-C 3 N 4 nanosheets) were fabricated through an electrostatic interaction route in an aqueous solution. The nanocomposites were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and transmission electron microscopy. Results showed that the g-C 3 N 4 nanosheets were decorated randomly by CdSe QDs, with average diameter of approximately 7 nm. The feasibility of the FRET system as a sensor was demonstrated by Hg (II) detection in water. At pH 7, a linear relationship was observed between the fluorescence intensity and the concentration of Hg (II) (0–32 nmol/L), with a detection limit of 5.3 nmol/L. The new detection method was proven to be sensitive for detecting Hg 2+ in water solutions. Moreover, the method showed high selectivity for Hg 2+ over several metal ions, including Na + , Mg 2+ , Ca 2+ , Pb 2+ , Cr 3+ , Cd 2+ , Zn 2+ , and Cu 2+ . The CdSe QDs/g-C 3 N 4 nanosheet conjugate exhibited desirable long-term stability and reversibility as a novel FRET sensor. The novel FRET-based fluorescence detection provided an attractive assay platform for quantifying Hg 2+ in complex water solutions.