An SU-8 microlens array fabricated by soft replica molding for cell counting applications

This paper reports a new polymeric, aspheric SU-8 microlens array using a soft replica molding method and its application to cell counting. A bio-detection system comprising the SU-8 microlens array with its three-dimensional convex geometry, a micro flow cytometer chip and an optical detection module is demonstrated. A polymethyl methacrylate (PMMA) template is first fabricated and then the SU-8 microlens array is replicated using a new fabrication process. The developed array has four sizes of microlens, with diameters of 50, 100, 150 and 200 νm. Experimental results show that the surface roughness of the microlens was only 10.2 nm for the SU-8 polymer material. The microlens had good surface uniformity and excellent optical properties with calculated focal lengths ranging from tens to hundreds of micrometers, depending on their dimensions. A microlens with a high numerical aperture ranging from 0.3 to 0.75 was achieved. The microlens array can be used to increase the efficiency of the optical detection, allowing high-resolution detection and providing a high signal-to-noise ratio. The microlens array has the potential to be widely used for optical or biophotonic applications and for the integration of microfluidic devices. In order to demonstrate its capability, the developed microlens array was integrated with a micro flow cytometer for cell counting applications. Successful counting of fluorescent-labeled human lung cancer cells is demonstrated using the developed method. © 2007 IOP Publishing Ltd.