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A MEMS flow cytometer with integrated out-of-plane microlens and 3-D hydro-focus unit

This paper presents a micro flow cytometry device fabricated using Ultra Violet (UV) lithography of the negative tone photo resist SU-8. A diamond-shaped sample injection nozzle, a three-dimensional hydro-focusing unit, and an optical detection unit with integrated out-of-plane microlens were fabricated using tilting lithography techniques. In addition to a 60° horizontal focusing angle, 30° slopes were designed and fabricated in the vertical direction of the hydro-focusing chamber. This unique design makes the hydro-focusing unit presented in this paper a truly three-dimensional one instead of the two-dimensional ones usually reported in literature. In the optical detection unit, a multi mode optical fiber was used to collect fluorescent or scattering light from the sample. To improve detection efficiency, out-of-plane microlens made of cured SU-8 polymer was imbedded in one of the outlet fluid channel walls. Numerical simulations were conducted to analyze the optical system and optimize the distances between optical elements to achieve best light coupling efficiency using commercial optical design software Zemax.