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Graphene quantum dots (GQDs) are promising for bioimaging applications due to their unique optical properties and good biocompatibility. However, the facile synthesis of GQDs with long-wavelength emission and high quantum yield (QY) under long-wavelength excitation is still a challenge. Herein, dual-emissive GQDs were synthesized via a facile one-pot solvothermal method using 2,7-dihydroxynaphthalene (2,7-DHN) and piperazine anhydrous (PA) as the raw materials. The obtained GQDs exhibited a green-emission band (core state emission) and a red-emission band (surface state emission), which originated from the inner π-conjugated structure and various surface functional groups, respectively. The π-conjugated structure mainly comes from the aromatic rings in 2,7-DHN, and the N–H of PA acts as the main nitrogen source, which is beneficial for the QY. The obtained GQDs showed obvious concentration-dependent optical properties. Importantly, they are able to generate red emission with a high absolute QY of 54.9% in ethanol and 24.9% in water, among the best values of reported GQDs. In addition, the prepared GQDs have good water-solubility, low cytotoxicity, and superior stability against photobleaching. Based on the above advantages, the as-prepared GQDs were successfully applied for labeling HeLa cells in vitro. Therefore, our prepared GQDs demonstrated that they can be an efficient biomarker for fluorescent bioimaging. [ABSTRACT FROM AUTHOR]

We report the synthesis of a novel type of carbon-based nanostructure, which is composed of a string of carbon nanopearl chains (CNPCs) with a connection structure of carbon nanofibers using a chemical vapor deposition method. Regularly spaced, nanometer-sized balls of graphitic carbon are found on the amorphous nanofibers. The nanopearls have nanometer-sized spheres, bodies in diameter varying from tens of nanometers to hundreds of nanometers, with solid interiors. The chain connections have a length ranging from several nanometers up to micrometers between two nanopearls. The nanopearls connect each other by the nanofibers, thus forming a chain. The CNPCs have potential for use as reinforcing matrix to produce strong and tough carbon-based nanocomposites. [ABSTRACT FROM AUTHOR]