Microflow cytometer incorporating sequential micro-weir structure for three-dimensional focusing

A novel microflow cytometer is proposed in which the sample stream is focused initially in the horizontal (X–Y) plane by two sheath flows and is then focused in the vertical (Y–Z) plane by a sequential micro-weir structure before entering the detection region of the device. The proposed device is fabricated using a modified glass fabrication process, and is then characterized both numerically and experimentally using fluorescent polystyrene beads with diameters of 7 and 15 lm, respectively. The experimental and numerical results confirm the effectiveness of the hydrodynamic sheath flows in centralizing the particles in the horizontal plane prior to entering the sequential micro-weir structure. Furthermore, it is shown numerically that the micro-weir structure confines the particle stream to the center of the vertical plane such that the particles pass through the detection region in a oneby-one fashion can be counted with a high degree of reliability. The experimental results confirm that the proposed 3-D focusing scheme enables the fluorescent beads with different diameters to be reliably sorted and counted.