Microfabrication of an integrated optical cell counter for cytometry application

Abstract

This paper presents the design and fabrication of an integrated cell counter for a MEMS flow cytometer. The imbedded out-of-plane micro lens in the cell counter is used to focus the fluorescent or scattering light emitting from the dyed cells into the output fiber to improve the optical detection efficiency. Both the optical cell counter device with imbedded micro-lens and the hydro-focusing unit of the micro flow cytometer were fabricated using a process based on UV lithography of SU-8 negative-tone photoresist. A novel microfabrication technology based on tilted UV-lithography and controlled exposure dosage and development time was performed to produce the out-of-plane micro lens. Out-of-plane micro lens with various pad sizes and focal lengths can be fabricated by carefully controlling the fabrication process. The microlens and the hydrofocusing unit were fabricated using the same mask. High alignment accuracy can therefore be achieved without any post-fabrication alignment processes.