Highly biocompatible graphene quantum dots: green synthesis, toxicity comparison and fluorescence imaging

Graphene quantum dots (GQDs) have tremendous potential in biological imaging due to their bright visible photoluminescence mission. However, the tedious preparation procedures and potential toxicity of GQDs greatly limit their application in biological field. Here, highly biocompatible GQDs (HGQDs) have been successfully prepared only by glucose in aqueous solution. Compared with GQDs prepared from conventional methods (CGQDs), the cytotoxicity of HGQDs reduced by more than 60%, and the flow cytometric analysis of the normal cells treated with HGQDs showed that the early and late apoptotic rate reduced by more than 72% and 40%, respectively. In vitro fluorescence imaging showed that both cells and bacteria could be imaged by HGQDs, and the morphology of cells and bacteria could be kept to a maximum extent. A long-term in vivo study revealed that no obvious organ (heart, liver, spleen, lung and kidney) damage or lesions were observed, and the blood–brain barrier (BBB) could be overcome, which provides the possibility for treatment and diagnosis of brain-related diseases. With adequate studies of biocompatibility, both in vitro and in vivo, HGQDs may be considered for further biological application.