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.

Excellent biocompatibility of liquid metals is the basis for developing biomedical applications, such as implantable devices, drug delivery, and tumor therapy. Especially, a systematic study to reveal the influence of gallium-based liquid metals on the composition of blood while they are used in the human body is vital but missing. Here, the compatibility of three kinds of frequently used gallium-based liquid metals with human blood and serum was explored systematically. The results show that treating blood and serum with gallium-based liquid metals did not cause hemolysis, suggesting red blood cells are not damaged or ruptured, and treatment had a negligible effect on the components in the blood. Additionally, the serum levels of glucose, cholesterol, and liver function molecules showed no change after adding liquid metals. These findings suggest that liquid metals have high compatibility with human blood and serum and are conductive to be applied in the fields of biomedical engineering.