Noninvasive in vivo diagnosis of brain glioma using RGD-decorated fluorescent carbonaceous nanospheres

Fluorescent carbonaceous nanospheres (CDs) have gained significant attention because of their promising applications, especially in biology and medicine, due to their unique properties. However, the application of CDs in the noninvasive imaging of diseased tissues has been restricted by the poor targeting efficiency of CDs. In this study, CDs were prepared from sucrose and glutamic acid with a particle size of 122.5 nm. Due to quantum confinement in the nanoparticles, CDs exhibited emission from 450 to 600 nm upon excitation at approximately 400 nm. This feature made it possible to use the CDs for low-background bioimaging of deep diseased tissues. RGD, a ligand that can target α_vβ₃, which is highly expressed on most tumor and neovascular cells, was decorated onto the CDs after PEGylation. The product, RGD-PEGCDs, possessed low cytotoxicity, as determined by MTT assay. In vitro, RGD-PEG-CDs targeted U87 (a human brain glioma cell line) cells with a higher cellular uptake intensity than CDs and PEGylated CDs (PEG-CDs), and endosomes were involved in the uptake procedure. The internalization of RGD-PEG-CDs, PEG-CDs and CDs all were primarily mediated by macropinocytosis and a clathrin-mediated pathway, which were energy-dependent. Additionally, the uptake of RGD-PEG-CDs could be significantly inhibited by free RGD, indicating that the uptake was mediated by the receptor of RGD. In vivo, RGD-PEG-CDs accumulated in U87 glioma at high intensity, at values that were 1.67- and 1.64-fold higher than those of PEG-CDs and CDs. Furthermore, RGD-PEG-CDs exhibited good colocalization with neovasculature. In conclusion, RGD-PEG-CDs could be successfully used for noninvasive U87 glioma imaging.