A novel magnetic fluorescent biosensor based on graphene quantum dots for rapid, efficient, and sensitive separation and detection of circulating tumor cells.

We describe a "turn-on" magnetic fluorescent biosensor based on graphene quantum dots (GQDs), Fe3O4, and molybdenum disulfide (MoS2) nanosheets. It is used for rapid, efficient, and sensitive separation and detection of circulating tumor cells (CTCs). A facile approach (electrochemical synthesis method) for the preparation of photoluminescent GQDs functionalized with an aptamer [epithelial cell adhesion molecule (EpCAM) receptors] and a magnetic agent for one-step bioimaging and enrichment of CTCs is described. MoS2 nanosheets, as a fluorescence quencher, and the aforementioned aptamer@Fe3O4@GQD complex were assembled to construct "turn-on" biosensing magnetic fluorescent nanocomposites (MFNs). This system exhibits low cytotoxicity and an average capture efficiency of 90%, which is higher than that of other magnetic nanoparticles on account of the one-step CTC separation method. In addition, the MFNs could quickly identify and label CTCs within 15 min, surpassing other one-step and two-step marker detection methods. Furthermore, because of the presence of aptamers, the MFNs have specific capability to capture CTCs (both low- and high-EpCAM-expressing cells). In addition, high-sensitivity detection of up to ten tumor cells in whole blood was achieved. Therefore, the MFNs have great potential to be used as universal biosensing nanocomposites for fluorescence-guided tumor cell enrichment and bioimaging. Graphical abstract ᅟ.