Design, fabrication, and test of an on-chip micro flow cytometer with integrated out-of-plane microlenses

A micro flow cytometer with an integrated three-dimensional hydro-focusing unit and out-of-plane microlenses was successfully fabricated and tested. The entire system was fabricated with SU-8 ultra-violet lithography process. In the hydro-focusing unit, sheath flows pass through a trapezoid-shaped chamber with three 30° slopes to focus the sample flow in both horizontal and vertical directions. As an essential component in the on-chip optical detection system, integrated out-of-plane microlens was embedded in the sidewall of the fluid outlet channel in the detection area. A pre-aligned optical fiber holder was fabricated on chip to fix the output optical fiber in a position aligned to the microlens. Optical simulation and analysis were also conducted using commercial software Zemax. Numerical simulation results confirmed that the use of microlens substantially improved the detection efficiency by focusing the fluorescent light from the sample cells into the output optical fiber. Preliminary cell counting experiment was performed using the fabricated micro flow cytometer system and the experimental results proved the feasibility of the integrated micro flow cytometer design.