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Boron-doped graphene quantum dots (B-GQDs) are prepared via a one-pot acid-free microwave approach with graphene oxide as the carbon source and borax as the boron source. Boron atoms are incorporated into the graphene framework by attacking the defects in the graphene structure, deriving an atomic percentage of 1.44% in the final product. Boron atom doping into the graphene structure and restoration of defects in the graphene structure bring the obtained B-GQDs favorable photoluminescence behaviors. The as-prepared B-GQDs exhibit excitation-independent photoluminescence behaviors with an excitation/emission maximum at 320/430 nm, and a fluorescence quantum yield of 21.1%. Moreover, stable photoluminescence is observed within a wide range of pH 3.0–11.0. A tolerance to an external ionic strength of up to 2.0 mol L−1 KCl along with an excellent anti-photobleaching capability is achieved. The standard MTT assay suggests that the B-GQDs are of low cytotoxicity with favorable biocompatibility, and a cell viability of 87% could be achieved at 4.0 mg mL−1 of B-GQDs. The practical application of B-GQDs in bio-analysis is demonstrated by bio-imaging of HeLa cells. [ABSTRACT FROM AUTHOR]

The regulation of hydrophilicity/hydrophobicity of carbon dots (CDs) at will is most important. One pot simultaneous preparation of hydrophilic and/or hydrophobic CDs is herein reported, via a hydrothermal process with 1-butyl-3-methylimidazolium hexafluorophosphate as the carbon source in a H3PO4–ethanol medium. The hydrophilicity or hydrophobicity of CDs (or their proportions) is simply regulated by varying the H3PO4/ethanol molar ratio. Hydrophilic and hydrophobic CDs are obtained simultaneously with H3PO4/ethanol molar ratios within 0–1.72, while hydrophilic or hydrophobic CDs are the sole product obtained from H3PO4–BmimPF6 or BmimPF6-only systems. The CDs exhibit excitation-dependent maximum fluorescence at 360/440 nm (hydrophilic) and 430/510 nm (hydrophobic), with quantum yields of 17.0% and 7.7%, respectively. Both hydrophilic and hydrophobic CDs obtained by this approach exhibit favorable biocompatibility and offer great potential in bio-imaging as demonstrated for the fluorescent labeling and imaging of live HeLa cells. [ABSTRACT FROM AUTHOR]