Abstract
Graphene quantum dots (GQDs) have been developed as promising optical probes for bioimaging due to their excellent photoluminescent properties. Additionally, the fluorescence spectrum and quantum yield of GQDs are highly dependent on the surface functional groups on the carbon sheets. However, the distribution and cytotoxicity of GQDs functionalized with different chemical groups have not been specifically investigated. Herein, the cytotoxicity of three kinds of GQDs with different modified groups (NH2, COOH, and CO-N (CH3)2, respectively) in human A549 lung carcinoma cells and human neural glioma C6 cells was investigated using thiazoyl blue colorimetric (MTT) assay and trypan blue assay. The cellular apoptosis or necrosis was then evaluated by flow cytometry analysis. It was demonstrated that the three modified GQDs showed good biocompatibility even when the concentration reached 200 μg/mL. The Raman spectra of cells treated with GQDs with different functional groups also showed no distinct changes, affording molecular level evidence for the biocompatibility of the three kinds of GQDs. The cellular distribution of the three modified GQDs was observed using a fluorescence microscope. The data revealed that GQDs randomly dispersed in the cytoplasm but not diffused into nucleus. Therefore, GQDs with different functional groups have low cytotoxicity and excellent biocompatibility regardless of chemical modification, offering good prospects for bioimaging and other biomedical applications.
Highlights
Quantum dots have been widely applied in the biomedical field due to their various advantages such as sizedependent optical properties, high fluorescence quantum yields, and excellent stability against photobleaching [1,2,3]
The UV–Vis absorption spectra of NH2-graphene quantum dots (aGQDs) showed characteristic peak at around 230 nm and the absorption intensity decreased with the increasing wavelength, which was consistent with the previous report [6]
The present study investigated the cell distribution of three Graphene quantum dots (GQDs) modified with different functional groups and compared their cytotoxicity in A549 and C6 cells
Summary
Quantum dots have been widely applied in the biomedical field due to their various advantages such as sizedependent optical properties, high fluorescence quantum yields, and excellent stability against photobleaching [1,2,3]. Graphene quantum dots (GQDs), a kind of zerodimensional material, have the same single-atom layer as graphene but their lateral dimensions are less than 100 nm [13,14,15,16] Owing to their high surface area and good biocompatibility, GQDs have the potential to be vectors for delivery protein or drug molecules to cells [6,12,17,18,19]. Beyond that, when functionalized with different chemical groups, GQDs can be used to build multifunctional structure through combining with various other materials such as protein, drug molecules, and nanotubes by covalent linkage, which will extend their widespread applications in biomedical field [18,22,23] Jing and his colleagues have fabricated multifunctional core-shell structure capsules composed of olive oil, dual-layer porous TiO2 shell, Fe3O4, and GQDs [23]. GQDs with different functional groups have excited extensive and increasing research interest
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