The on-off-on Fluorescence Sensor of Hollow Carbon Dots for Detecting Hg and Ascorbic Acid.

Carbon dots (CDs) have excellent fluorescence properties and can be used in many research fields. In this paper, carbon dots were prepared by microwave-assisted pyrolysis of citric acid and urea, characterized by transmission electron microscope (TEM), X-ray diffractometer (XRD), C-NMR spectrum, zeta potential, Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV-vis) absorption and fluorescence spectra, and detected the Hg and ascorbic acid (AA) sequentially. It showed that carbon dots were hollow, spherical particles and less than 10 nm, photoluminescence quantum yield of carbon dots was about 15%. The CDs were selective and sensitive to Hg and AA based on the "on-off-on" fluorescence behavior. The detection limits of CDs for Hg and AA were 0.138 μM and 0.212 μM, respectively. Fluorescence response mechanism of CDs was also discussed.