A simple dynamic optical manipulation technique for label-free detection of biological cells

A dynamic optical tweezers system is employed for generation of an optical trap in continuous rotation for manipulating a biological cell in an aqueous solution. When the rotating speed is increased, the trapped cell experiences an augmented viscous drag force, and eventually it escapes from the trap at the critical rotating speed: when the drag force is greater than the trapping force. With experimental verifications, the method can easily be employed to differentiate cells in terms of trapping forces due to different refractive indices. The proposed method is a simple, robust, accurate and noninvasive label-free technique for cell detection.