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.