Microfluidic Channel Design for Circulating Tumor Cell Analysis

A straight microfluidic channel of 100 μm width and 50 μm height was used, and thus the aspect ratio was defined as 1/2 (AR = height/width). The length of the main channel was 25 mm and the width of the expansion region at the outlet trifurcation was 800 μm for visualization of the flow streams of particles and cells. At the entrance region of the microchannel, micropillars of 50 μm width and 100 μm length were designed with 50 μm spacing to avoid the possible blockage of the microchannel by aggregated particles or CTC clusters. In clinical samples, CTC clusters can be found in approximately 5–20% of the total CTCs [43 (link),44 (link)].
A polydimethylsiloxane (PDMS) microfluidic channel was fabricated using standard soft-lithography techniques with a replica mold, which was fabricated using an SU-8 negative photoresist (MicroChem, Newton, MA, USA) on a silicon wafer. A 10:1 mixture of the PDMS base and curing agent (Sylgard 184, Dow Corning, Midland, MI, USA) was cast over the replica mold, degassed in a vacuum chamber, and baked in an oven at 80 °C for 1 h. The cured PDMS channels were peeled off from the mold and bonded on a glass slide with oxygen plasma (CUTE, Femto Science, Gyeonggi, Korea). To minimize unwanted hydrophobic interactions between polystyrene particles and the channel surface, the PDMS channel was treated with Tween 20 [45 (link)].