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Cell adhesion forces have been of interest since the 1920’s. These forces are estimated to be in the nano-Newton range, which is inaccessible to the majority of optical tweezers systems, so most studies use direct contact methods such as atomic force microscopy or micropipettes. In the case of weakly adhered cells such as biflagellated plant cells attached to a coverglass surface, separation does seem possible with the use of an optical trap system. We report the detachment of microalgae Dunaliella tertiolecta from the top and bottom of a coverglass sample chamber using a single nearinfrared CW trapping laser focused with an underfilled high numerical aperture microscope objective. We show that the time required for detachment of a cell is dependent on the incident laser power, taking 3 seconds for a power of 319 mW, and about 90 seconds for a power of 41 mW. We are able to hold the cell in the optical trap after being detached using the same laser beam. The cells detached from the bottom were levitated at an equilibrium position determined by the incident power, while the ones on the top were held in the trap against the top surface. After the cells were released, they were seen to be unaffected in their motion. One advantage of our described method is that, from the large range of sizes of the microalgae within the prepared sample chamber, we are able to select a specific size for further studies.
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