One-step synthesis of fluorescent hydroxyls-coated carbon dots with hydrothermal reaction and its application to optical sensing of metal ions

Carbon dots (CDs) with average diameter of 3.1 +/- 0.5 nm were facilely synthesized with candle soot through hydrothermal reaction in sodium hydroxide aqueous solution. The as-prepared CDs were covered with a lot of hydroxyls, possessed properties of good water-solubility, anti-photobleaching, salt tolerance, and low cytotoxicity, and had a fluorescence quantum yield (QY) of about 5.5%. The fluorescence of the hydroxyls-coated CDs could be selectively quenched by metal ions such as Cr3+, Al3+ and Fe3+, which is because these metals can easily combine with the hydroxyl groups on the surface of CDs and induce aggregation of hydroxyls-coated CDs. Experiments showed that the quenching of Cr3+ had a Sterm-Volmer constant of 1.03 x 10(7) M-1 with a liner range of 1.0-25.0 mu M and detection limit of 60 nM (3 sigma).