Nitrogen and phosphorus co-doped graphene quantum dots: synthesis from adenosine triphosphate, optical properties, and cellular imaging

Abstract

Graphene quantum dots (GQDs) are emerging zero-dimensional materials promising a wide spectrum of applications, particularly, as superior fluorescent reporters for bio-imaging and optical sensing. Heteroatom doping can endow GQDs with new or improved photoluminescence properties. Here, we demonstrate a simple strategy for the synthesis of nitrogen and phosphorus co-doped GQDs from a single biomolecule precursor (adenosine triphosphate - ATP). Such ATP-GQDs exhibit high fluorescence quantum yield, strong two-photon upconversion, small molecular weight, high photostability, and good biocompatibility. Furthermore, transferrin conjugated ATP-GQDs have been used for imaging and real-time tracking of transferrin receptors in live cells.

Recent Advances in Graphene Quantum Dots as Bioimaging Probes

“…Also, nitrogen and sulfur co-functionalized GQDs are successfully obtained using nitrogen and sulfur containing compounds of 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl) imide [68], polythiophene [136] and thiourea [110]. Moreover, o-dichlorobenzene [128], ATP [119,120] and 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide [68] are utilized as sources to prepare chloride-, phosphorus-and fluoride-functionalized GQDs, respectively. The dimensions and heights of graphene sheets in the obtained GQDs range from 1.5 to 100 nm and 0.5 to 5 nm, respectively.…”

“…Because of their low cost and easy availability, natural resources such as coffee grounds [100], cow milk [101,102] and neem leaf extract [103] are used to fabricate fluorescent GQDs by hydrothermal or microwave irradiation strategies. Low-cost organic compounds, such as citric acid [104][105][106][107][108][109][110][111][112], acetylacetone [113], glucose [114][115][116][117], fructose [118], ethylene diamine tetraacetic acid (EDTA) [119], adenosine 5′-triphosphate disodium salt (ATP) [119,120], glutamic acid [121] and humic acid [122], are also the most commonly used starting materials for the synthesis of GQDs either via pyrolysis or microwave irradiation or hydrothermal/solvothermal treatment. Moreover, due to their similarity in structure, polycyclic aromatic hydrocarbons are generally regarded as nanoscaled fragments of graphene, which gives them great promise for preparing monodispersed GQDs with precisely tailored structure, morphology and size.…”

“…5a), and the internalized ATP-GQDs scatter in the cytoplasm from the confocal microscopy images. In [120]. Reprinted with permission from ref.…”

“…HeLa cells after incubation with as-prepared B-GQDs are found to show bright blue photoluminescence by excitation at 330 nm, further indicating that B-GQDs can serve as useful candidates for bioimaging agents for living cells. In another work, Arundithi et al [120] prepared nitrogen and phosphorus co-doped GQDs (ATP-GQDs) from a single biomolecule precursor (adenosine triphosphate, ATP) via carbonization and subsequent chemical exfoliation methods. Interestingly, because of the co-existence of electron-withdrawing and -donating sites (which can form p-n type photochemical diodes) in heteroatom-doped ATP-GQDs, they exhibit good two-photon excitation properties.…”

“…Reprinted with permission from ref. [120]. Copyright 2015 Royal Society of Chemistry comparison with transferring conjugated GQDs (Tr-GQDs) ( Fig.…”