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Fexible polydimethylsiloxane/multi-walled carbon nanotubes (PDMS/MWCNTs) membranous metacomposites with negative permittivity.

1–3 nm nitrogen‐doped graphene quantum dots with quantum yield of 0.74 are synthesized via cutting graphene oxide and in situ doping. The size is determined by the remaining graphitic domains of precursor. The doping mechanism is illustrated, and the dominant photoluminescence factor is experimentally confirmed to be the n–π* transition between the lattice‐doped nitrogen and the conjugate structure of graphene.

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.