Label-free continuous cell sorter with specifically adhesive oblique micro-grooves

We report the development of a label-free continuous cell sorting method based on specific adhesivity between cells and surface-immobilized adhesion molecules. The separation of cells is induced by cross-flow adhesive force on micron-sized stripes with adhesion molecules immobilized on the surface. In order to accurately form the adhesive stripes on a microchannel wall, 1 µm wide micro-grooves are fabricated at a certain angle with respect to the flow direction using direct electron-beam lithography. Amino-functionalized parylene is used as the groove surface material, and streptavidin is immobilized on the entire surface, resulting in a surface with periodic adhesive patterns. The effectiveness of the proposed cell sorting principle is verified by flow-through experiments using functionalized particles as model cells. Measurements of the motion of biotin-coated microparticles show that the particles decelerated by specific adhesivity are displaced in the cross-flow direction. The observed cross-flow displacement is around 0.8% of the streamwise travelling distance. It is also shown that the rate of cross-flow displacement is independent of the flow rate or the stripe angle. Finally, it is demonstrated that a mixture of streptavidin- and biotin-coated microparticles can be completely separated after flowing over a 20 mm long patterned surface. The proposed label-free continuous lateral separation scheme has a wide range of potential applications for separation of cells which could not be distinguished by size or separated using dielectric forces.