Nitrogen–Sulfur-Doped Graphene Quantum Dots with Metal Ion-Resistance for Bioimaging

Abstract

The development of ultrastable and highly fluorescent heteroatoms-doped graphene quantum dots (GQDs) for bioimaging remains a challenge due to the fluorescence quenching caused by binding between the heteroatoms-based functional groups of the GQDs and common metal ions in biological systems. Here, we developed a facile hydrothermal method to prepare nitrogen−sulfur doped GQDs (NS-GQDs). The fluorescence signals of the NS-GQDs are highly stable in the existence of different metal ions. Two natural products, aspartic acid and cysteine, were utilized as the carbon precursors and heteroatomic (nitrogen and sulfur) sources. The produced NS-GQDs showed a quantum yield up to 19.3 ± 1.7% with a maximum emission of 480 nm under the excitation of 400 nm. The elemental analysis, including X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS), and Fourier-transform infrared spectroscopy (FTIR), were performed to characterize the composition and surface groups of NS-GQDs. Additionally, the NS-GQDs not only showed notable photostability, but also thermostability and chemical stability. Moreover, the NS-GQDs demonstrated very low cellular cytotoxicity in vitro. Finally, the NS-GQDs were applied for fluorescence imaging of cells, which also exhibited excellent fluorescent stability even with treatment of copper ions. The results indicated that the developed novel NS-GQDs have a promising potential to be used as ultrastable fluorescent agent in the field of bioimaging and biosensing.

Research advance on cell imaging and cytotoxicity of different types of quantum Dots

“…Reproduced with permission from Ref. (Schroer et al, 2019). Copyright 2019 American Chemical Society.…”

“…In recent years, due to the great potential of GQDs and Cdots in the field of bioimging, scientists have made great efforts to improve their fluorescence properties, such as doping nitrogen or sulfur into these QDs (Lu, Li, Dong, & Wei, 2019; Shi et al, 2019). However, the fluorescence is easily quenched by metal ions, which is one of the challenges of biological imaging of carbon‐based QDs (Schroer et al, 2019). Fortunately, scientists are improving their properties step by step.…”

“…Fortunately, scientists are improving their properties step by step. Recently, Schroer et al (2019) synthesized a kind of nitrogen and sulfur doped GQDs (NS‐GQDs), which can resist the quenching of metal ions. As shown in Figure 2A, the fluorescence intensity of the polymerdots (Pdots) used for comparison is greatly quenched in the presence of Cu ions, while the fluorescence intensity of NS‐GQDs is not affected by Cu ions.…”

Hydrothermal synthesis of blue‐green emitting carbon dots based on the liquid products of biodegradation of coal

“…In brief, the CDs synthesized in our study showed outstanding photo‐, ions‐ and time‐stability, providing particularly suitable for practical applications including bio‐imaging, anticounterfeiting, biomedicine, sensor, and so on. The high‐stability of CDs is due to various functional groups attached to the surfaces of CDs 60,65 …”

“…The high-stability of CDs is due to various functional groups attached to the surfaces of CDs. 60,65…”