Robotic manipulation of a biological cell using multiple optical traps

Existing control techniques for optical tweezers utilize a single focused laser beam to directly trap and manipulate a target cell. However, a typical force generated by an optical trap is extremely small (few pico-newtons) and therefore it is not sufficient to manipulate a larger cell or object. The optical trap is also sensitive to the shape of the biological cell and the refractive index. Therefore, current automatic control techniques for optical tweezers cannot be used to manipulate a large cell or cell with irregular shape. In addition, excessive irradiation of the laser beam to the cell may also cause photodamage of even lead to death of the cell. In this paper, we propose a robotic control technique for optical tweezers to achieve automated manipulation of cell, which is beyond the capability of a single optical trap. First, multiple laser beams are generated, and each laser beam is used to trap one micro-particle to create a formation around the target cell to hold it. Then the target cell is manipulated to a desired position by controlling the motorized stage. The proposed control technique is particularly suitable for automated manipulation of sensitive biological cells, cells with large size or cells of irregular shape. Rigorous mathematical formulations have been developed to analyze the control system for automated cell manipulation. Experimental results are presented to illustrate the performance of the proposed controller.