UC San Diego

Optical tweezers and scissors are two common applications of laser micro-beams in biological research. Previously in our lab, there have been experiments that utilized both optical trapping and cutting, but in these experiments, optical trapping and cutting were performed at different time-points as the sample would have to be transferred from an optical cutting system to an optical trapping system or vice versa. In this project, we designed and built a combined laser scissors and tweezers microscope that (1) has two trapping beams and (2) uses a short pulsed tunable 200 fs 76 MHz 710-990 nm Ti:Sapphire laser for laser microsurgery. Both the position and power of all three beams can be independently controlled. Moreover, experiments were performed to test the ability of the system to trap and move whole chromosome or chromosome fragments inside living PTK-2 cells as well as chromosomes in suspension. The optical scissors laser was used at 730 nm to successfully cut chromosomes inside live cells. The optical traps were able to move whole chromosomes or chromosome fragments (after cutting) inside live Nocodazole-treated cells and also chromosomes isolated in suspension. The optical traps were not able to move intact or cut chromosomes inside un-treated cells, cold-treated cells or cells where the kinetochore or microtubule spindle was damaged using the optical scissors. Our experiments show that chromosome's geometry and index of refraction allow for easy trapping. However, when inside cells, the microenvironment around them, especially the microtubule spindle cage, can prevent any trapping movement