Tailoring color emissions from N-doped graphene quantum dots for bioimaging applications

• Published in: Light, science & applications Vol. 4; no. 12; p. e364
• Main Authors: Qu, Dan, Zheng, Min, Li, Jing, Xie, Zhigang, Sun, Zaicheng
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-12-2015; Springer Nature B.V
• Subjects: 639/624/399/354; 639/624/399/918/1054; Applied and Technical Physics; Atomic; Classical and Continuum Physics; Color; Emission; Emission spectroscopy; Fluorescence; Graphene; Lasers; Molecular; Optical and Plasma Physics; Optical Devices; Optics; original-article; Photonics; Physics; Physics and Astronomy; Quantum dots; Solvents; Tuning; nitrogen doped; pure color emission; excitation wavelength independent; graphene quantum dots
• ISSN: 2047-7538; 2047-7538
• DOI: 10.1038/lsa.2015.137

Unlike inorganic quantum dots, fluorescent graphene quantum dots (GQDs) display excitation-dependent multiple color emission. In this study, we report N-doped GQDs (N-GQDs) with tailored single color emission by tuning
π
-conjugation degree, which is comparable to the inorganic quantum dot. Starting from citric acid and diethylenetriamine, as prepared N-GQDs display blue, green, and yellow light emission by changing the reaction solvent from water, dimethylformamide (DMF), and solvent free. The X-ray photoelectron spectroscopy, ultraviolet-visible spectra results clearly show the N-GQDs with blue emission (N-GQDs-B) have relatively short effective conjugation length and more carboxyl group because H
2
O is a polar protic solvent, which tends to donate proton to the reagent to depress the H
2
O elimination reaction. On the other hand, the polar aprotic solvent (DMF) cannot donate hydrogen, the elimination of H
2
O is promoted and more nitrogen units enter GQD framework. With the increase of effective
π
-conjugation length and N content, the emission band of N-GQDS red-shifts to green and yellow. We also demonstrate that N-GQDs could be a potential great biomarker for fluorescent bioimaging.
Graphene quantum dots: solvents used to tailor emission color
Nitrogen-doped graphene quantum dots emitting blue, green, or yellow light are promising biomarkers for fluorescence bioimaging. Dan Qu and colleagues in China tailored the emission color of the quantum dots by changing the reaction solvent used in their fabrication. Dots prepared from protic solvent-emitted blue (450 nm) light, those prepared with aprotic solvent emitted green (550 nm), and solvent-free dots emitted yellow (580 nm). The emission colors were pure and narrow band with full-width half-maximum values of 71, 86, and 111 nm and decay lifetimes of 14, 13, and 10 ns, respectively. Imaging experiments with a confocal fluorescence microscope and A549 cells labeled with the graphene dots demonstrated that the cells did indeed become brightly illuminated with visible colors when optically excited, suggesting that the graphene dots are suitable for bioimaging.