Immuno-capture of cells in open microfluidics: Microfluidic probes integrated with herringbone micro-mixers

Effective capture of cancer cells from whole peripheral blood samples, i.e. circulating tumor cells (CTCs), is still an existing limitation for liquid biopsy-based diagnostics. The well-established closed-channel herringbone micro-mixers are one of the widely adopted methods for isolating CTCs based on antigen-antibody interaction. However, they are known to be associated with several drawbacks, such as limited capture areas within the channels, restricted access to isolated cells, difficulties to achieve multiplexed antibody capture assays for immuno-phenotyping, and limited postprocessing possibilities. To tackle these issues, we developed a novel microfluidic probe (MFP) that is integrated with herringbone micro-mixers on its tip surface (HMFP). The tip surface was designed with 2-slitted apertures, one for injecting the cell suspension and the other for performing high flow rate aspiration to confine the flow. The herringbone mixing elements were distributed in-between the apertures for micro-mixing that enhances the CTCs capture on the antibodies-coated bottom glass surface. Unlike the closed herringbone chips, the functionalized bottom glass surface was kept large given the capacity for the MFP to work in scanning mode, and so it prevented cell capture saturation effect. Our MFP design and experimental setup showed a cell capture efficiency of 59-81% with flow rates of 0.6-2.4 mL/h. The capture of CTCs in an open microfluidic system allows for easy post-process and CTC analysis, such as single cell drug testing and mechano-phenotyping using atomic force microscopy.