Fabrication of carbon quantum dots via ball milling and their application to bioimaging

Carbon quantum dots (CQDs) with an average diameter of 3 nm, exhibiting blue photoluminescence, have been obtained from commercial conductive carbon black by a cost-effective and straightforward exfoliation method using dry ball milling in the presence of sodium carbonate. As a secondary abrasive medium, sodium carbonate provides effective exfoliation of carbon black with a high degree of CQD graphitization and plays an essential role in the functionalization of CQDs with oxygen groups. Due to the low toxicity of CQDs against HeLa cancer cells (cell viability above 90% at a CQD concentration of 200 μg cm−3) and the ability to penetrate cells and emit blue light, CQDs are possibly suitable for biological imaging of cells.