Fluorescent Nitrogen-doped Graphene Quantum Research Articles

Waste derived approach towards wealthy fluorescent N-doped graphene quantum dots for cell imaging and H2O2 sensing applications

Herein, we report the synthesis of a highly fluorescent nitrogen doped graphene quantum dots (N-GQDs) from waste precursors such as melamine sponge and arjuna bark via a microwave treatment and its functional and morphological characterization using various spectroscopy techniques such as optical, FTIR, XPS and TEM. The as-prepared aqueous N-GQD (dia. 2–3 nm) was used for the bio-imaging application using breast carcinoma cell line (MDA-MB-231) as a model, and the locations of all cells in the cytoplasm as well as nuclei were observed to stain brightly in blue fluorescent color successfully. In addition to that, the aqueous N-GQD showed fluorescence quenching behavior in the presence of hydrogen peroxide, which was exploited to sense H2O2, a probable toxin generated in the diseased cells. Importantly, the cell cytotoxicity was measured and found to be non-toxic (70% survival) to the MDA-MB-231 cells even at very high concentration (∼1.8 mg/ml) of the synthesized N-GQD. This study revealing excellent biocompatibility and imaging of the model cancer cells, and sensing of H2O2 by fluorescent quenching, indicates potential in-vivo cell culture applications of the prepared fluorescent N-GQD.

Solid-state fluorescent nitrogen doped graphene quantum dots with yellow emission for white light-emitting diodes

Light-emitting graphene quantum dots (GQDs) are widely investigated due to their distinct merits. However, GQDs generally suffer from aggregation-induced luminescence quenching, which means they are highly emissive in a solution state with uniform dispersion but dramatically quenched in a solid or aggregated state. This problem significantly limits the application of GQDs, partially in the solid-state light-emitting devices. In this report, we successfully developed a simple and efficient hydrothermal method for the production of nitrogen doped graphene quantum dots (N-GQDs) with strong solid-state fluorescence (SSF) by using citric acid and o-Phenylenediamine as precursors. Under the 365 nm UV light illumination, the produced N-GQDs in an aqueous state exhibit blue color, with a quantum yield of 58%. As the concentration of N-GQDs increases, the photoluminescence exhibits an obvious red-shift from blue to yellow. For the N-GQDs in solid state, yellow luminescence with a high photoluminescence quantum yield (PLQY) of 28% is achieved under the 405 nm excitation. Finally, via the simple adjustment of thickness and the concentration of N-GQDs in blue emitting InGaN chips, color converter is enabled by constructing white light-emitting diode (WLED) device with improved color rendering index (CRI) and correlated color temperature (CCT).

A Green and lower-temperature synthesis of two-color fluorescent nitrogen doped graphene quantum dots

Herein, the nitrogen-doped graphene quantum dots (N-GQDs) were produced by a facile thermal treating strategy at low temperature using citric acid (CA) and urea as the precursors. The as-prepared N-GQDs with different ratios of the precursors exhibited blue or green emission with relatively high quantum yield in the ethanol solution. While in the aqueous solution, the quantum dots displayed both blue and green emissions, which indicate two independent luminescent centers coexisted in the N-GQDs. Considering of the excellent absorption ability of the N-GQDs in the visible-light region, the N-GQDs was combined with titanium dioxide (TiO2) as the dye sensitizer. And, the products showed 16 times catalytic degradation ability than that of pure TiO2 for rhodamine B (RhB).