Circulating tumor cells (CTCs) are cancer cells shed from primary tumor and circulating in the peripheral blood. CTCs initiate secondary tumor colonies and result in more than 90% of cancer death. Isolation and enumeration of CTCs have exhibited promising clinical applications in cancer early diagnosis, prognosis and personalized therapy. However, owing to the extremely low rarity (as low as one CTC in one billion blood cells), CTCs isolation remains a great technical challenge. Current CTCs isolation approaches are based either on their biological properties, including immunoassay, magnetic-activated cell sorting, fluorescence-activated cell sorting, or physical properties, including filtering, inertial microfluidics, deterministic lateral displacement and etc. In general, biology-based techniques are characterized as high purity but low throughput; while physical property based techniques have advantages of low cost and high throughput. In this work, we reported the fabrication of a multilayer crossflow device and demonstrated the capability of isolating CTCs from whole blood based on lateral-flow filtration. The device was consisted of a filter membrane sandwiched between two microfluidic channel layers and fabricated with standard PDMS soft lithography and multilayer bonding technique. A 77.3% filtration efficiency with 4.5um polystyrene beads and a 97% cancer cells recovery rate have been achieved for a single-pass filtration. To further enhance the enrichment ratio(concentration of CTCs prior to filtration over that post-filtration) of CTCs over blood cells, a recirculating filtration system was built by combing the crossflow device with pressure pump and electromagnetic valves. In this system, 1 ml blood sample was treated for 10 times within 40 minutes, with an enrichment ratio of more than 104.
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