Selenium Doped Graphene Quantum Dots as an Ultrasensitive Redox Fluorescent Switch

A new reversible fluorescent switch for the detection of oxidative hydroxyl radical (•OH) and reductive glutathione (GSH) was designed based on the use of selenium doped graphene quantum dots (Se-GQDs). The Se-GQDs have a thickness of 1–3 atomic layers, a lateral size of 1–5 nm, a quantum yield of 0.29, and a photoluminescence lifetime of 3.44 ns, which ensured a high selectivity and stability for the fluorescent switch. The fluorescence of Se-GQDs was reversibly quenched and recovered by •OH and GSH, respectively, because of the reversible oxidation of C–Se groups and reduction of Se–Se groups. This brand-new GQD-based fluorescent switch gave a rapid response when tested in both aqueous solutions and living HeLa cells. In particular, the detection limit for •OH was only 0.3 nM, which was much lower than that in switches made from organic dyes.