Optical Tweezers: Autonomous Robots for the Manipulation of Biological Cells

Optical tweezers (OTs) are a popular tool for manipulating biological objects, especially cells [1], [2]. Using a tightly focused laser beam, they exert sufficient forces to tweeze, i.e., hold (trap) and move, freely diffusing cells in the vicinity of the beam focus. The beam can be focused at any point in the workspace, which is typically a liquid-filled glass slide. The trapped cell can, thus, be translated and rotated (transported) in three dimensions by changing the beam focus position. OTs provide certain advantages over other cell-manipulation techniques. They are able to manipulate cells with a greater degree of precision as compared with microfluidic flow. Significant contact forces are not exerted on the cells, unlike in mechanical manipulation, thereby avoiding damages due to contact friction or surface chemistry. The cells are also easily released at the end of the manipulation by simply switching off the laser beam. Hence, OTs have been extensively used for mechanical characterization of cells by measuring their viscoelastic properties to distinguish between normal and diseased cells [3]. They have also been used for separating cells of different types [4] and investigating the response of cells to external stimuli [5]. However, manual or teleoperated control of the laser beam has limited their applicability for multicellular studies.