Circulating tumor cells (CTCs) give a valuable insight into tumor progression and metastasis. Therefore, it is important to detect, capture, and analyze CTCs in the blood of patients with malignant tumors. In their review, Yong-Qiang Li and co-workers describe the unique biochemical and biophysical properties of CTCs and highlight novel materials for their detection and capture.
CTCs have a higher density and larger size than other blood cells, and they are less deformable. These biophysical differences can be used to capture CTCs in blood samples. CTCs are caught in microfluidic systems such as microfilters, arc-shaped array traps, or spiral microfluidic channels because of their stiffness and size. CTCs can also be captured due to interactions of surface receptors with antibodies. In recently developed systems, suitable antibodies are attached to the surface of micropost arrays and a herringbone chip.
By employing nanostructures (e.g., nanopillars, -wires, -fibers, -sheets, and -pores) in such capturing systems, the surface area is enhanced. Hence, the capture efficiency of the devices is improved. The highest capture efficiency of a nanostructure (80%) was achieved by combining micropores of reduced graphene oxide foam with ZnO nanorods.
Another recently developed method to detect and capture CTCs is micro-NMR. In this approach, CTCs are immunospecifically labeled by magnetic nanoparticles, which leads to a highly sensitive detection. Unfortunately, the surface of CTCs is very heterogeneous and, therefore, labeling efficiencies are low.
After capturing, CTCs have to be identified to determine their origin and genetic profile. Here, the problem of heterogeneity also occurs, since the cells are identified by fluorescent antibodies. Therefore, label-free microfluidic systems seem to be more promising for capturing CTCs. However, captured cells are often no longer intact because of high shear forces in such systems. For future developments in this area, single-cell capture and identification is a promising method to further understand the molecular characteristics of CTCs.
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