Optically induced flow cytometry for continuous microparticle counting and sorting

This paper reports a new microfluidic device capable of performing optically induced flow cytometry (OIFC). This enables it to continuously count and to sort microparticles based on optically induced dielectrophoretic (ODEP) forces. Gravity was used to drive the particles instead of using syringe pumps. The particles were then focused inside a sample channel by the ODEP forces and then passed through a detection region. A pair of optical fibers were embedded into fiber channels to count the number of particles and analyze the particle size in real time. Using 20.9 and 9.7 μm polystyrene microparticles, the average light intensity were about 63.67 and 8.80 units, with a coefficient-of-variation (CV) of 7.46 and 25.57%, respectively. This demonstrated that these two particle sizes could be successfully distinguished. After detecting the number and size of the microparticles, an optically induced dynamic switch (ODS) was used to sort microparticles to downstream fluidic outlets. The ODS used ODEP forces generated by different illumination intensities or optical line widths. The ODS was composed of two virtual electrodes which controlled particle movement in two dimensions. The ODS can successfully sort microparticles with different sizes continuously. The development of the OIFC device is a major advancement in the design of microparticle counting and sorting devices. Applications in future biomedical applications for cell counting and manipulation are envisioned.