Escape velocity sorting in optical tweezers system using a home-made piezo mirror

The flow of a fluid around an optically trapped particle forces the particle to move out of its equilibrium position. The particle will escape the trap if the fluid velocity exceeds a certain limit. Accordingly, we propose a novel and accurate method to sort the particles due to a difference in their escape velocities that depends on the size and refractive index of the particles. Here, the influence of the numerical aperture of the microscope objective and laser power on the escape velocities are studied for calibration. In addition, the method is used to sort various pairs of the particles; polystyrene beads with diameters of 1.48 and 2.18 micron, 1.65 and 3.0 micron, and 3.0 micron silica and polystyrene beads. The results show an efficiency of about 95% to locate the particles into the desired region. To verify the capability of the method for cell sorting, we have accomplished this technique to sort thalassemia red blood cells from healthy ones. Our presented method, as an accurate, high throughput and ease-of-use technique, could be used in the development of microfluidic-based devices and it is of critical importance to different areas in biotechnology and cellular biology.