Micromachine-based multi-channel flow cytometers for cell/particle counting and sorting

This paper reports a new micromachine-based flow cytometer capable of parallel processing of cell/particle counting and sorting using microfluidic technologies. Hydrodynamic focusing of multiple sample streams is first achieved by using a new layout of sheath flow channels coming from one single inlet port. Thus only one syringe pump is required during the operation. The flow rate of each sheath flow could be much more stable and uniform with this approach. The images of the focused multiple samples are then recorded downstream utilizing a high-speed digital CCD camera. The digital image processing technique is then used to count the number of the cells/particles. Theoretical models based on a 'flow-rate-ratio' method are used to predict the width of the multiple focused streams, which could be incorporated with a digital image processing system for cell/particle counting. Experimental data are found to be highly consistent with the theoretical results. Experimental data show that the developed device can successfully detect the number of cells/particles in two parallel sample streams and the velocities of the cells/particles in each cell line as well. Low counting error and high counting reliability are also verified by counting a mixture of polystyrene beads with different sizes. In addition, human red blood cells are used for the cell-counting test. Subsequently, cell/particle sorting could be achieved using dielectrophoretic (DEP) forces generated by built-in micro-electrodes downstream. Cell/particle sorting has been performed successfully using the DEP electrodes. The development of the multi-channel micro-flow cytometer could be crucial for the advancement of the cell-counting device.