Microsystems for Optical Cell Detection: Near versus Far Field

Optical flow cytometry is a process where physical and (bio‐) chemical parameters of single biological cells can be obtained in a flow‐through setup by optical measurement techniques. Unlike conventional systems, where measurements are conducted in the optical far field, the proposed system senses the cell's optical projection in the near field by using integrated photodiodes. This allows for the attainment of additional parameters, e.g., size and shape, which are usually hidden in the far field. In addition, parameters such as refractive index and absorption of the cell influence the sensor signal. Additionally, with another setup, a different approach is followed to measure similar parameters with external detection using a DVD laser pickup head and a microchannel equipped with a mirror. This low‐cost setup does not measure in the near field, and therefore, is dedicated to different parameters. In this contribution, results from measurements with polystyrene particles and biological cells (yeast and Chinese hamster ovary) are presented and the advantages and limitations of both systems are outlined.