Folic acid-conjugated carbon dots as green fluorescent probes based on cellular targeting imaging for recognizing cancer cells

Implementing visual detection of cancer cells has the potential to contribute greatly to basic biological research; early diagnosis of cancer is still a challenging issue. In this work, we designed and fabricated folic acid-conjugated fluorescent carbon dots (FA-CDs) for targeted imaging of cancer cells. The green fluorescent CDs were prepared by a facile hydrothermal treatment of dandelion as the carbon source and ethanediamine (EDA). The surfaces of the CDs possessed active amino groups for further covalent conjugation with FA. The uptake of FA-CDs into HepG-2 cells occurs via receptor-mediated endocytosis; this was confirmed by a comparative experiment using FR-negative (FR−) PC-12 cells as revealed by confocal laser scanning microscopy. Intracellular experiments demonstrated that the FA-CDs could accurately recognize positive FR (FR++/FR+) cancer cells in different cell mixtures of MCF-7/HepG-2 cells and HepG-2/PC-12 cells and could distinctly indicate the expression level of FR on the membranes of the cancer cells. The FA-CDs show excellent biocompatibility and low toxicity and may have great potential as an effective tool for accurately differentiating cancer cells from normal cells, in addition to cancer detection, prognosis, and individualized treatment.