With the advantages of non-physical contact, high precision, and efficiency, optical tweezers have been increasingly used to manipulate biological cells in various biomedical applications. When trapping a cell with optical tweezers, the cell must be located within the optical trap. The lack of an efficient control technique that can automatically control cell motion while consistently locating such cell within the optical trap causes the trapped cell to escape easily, thus resulting in the failure of the manipulation task. Therefore, the development of a unified controller that can Manipulate both cell trapping and cell motion simultaneously while possessing robustness to environmental disturbances is urgently needed. In this paper, we develop a novel unified controller that manipulates cell positioning and cell trapping simultaneously. First, we establish a geometric model to confine the cell within a local region around the optical trap. The connection between the cell and the optical tweezers is formulated by using the concept of cell-tweezers (C-T) coalition. Second, we develop a controller based on a defined potential field function to drive the C-T coalition to the desired state while avoiding collisions' with other obstacles in the environment. Finally, we perform experiments of transferring yeast cells to demonstrate the effectiveness of the proposed approach. (C) 2015 Elsevier Ltd. All rights reserved.