Physics 111 Advanced Laboratory. Professor Jan Liphardt This video accompanies the Optical Trapping Experiment, providing students with an introduction to the theory, apparatus, and procedures. An optical trap or optical tweezers is a device used to apply pico-newton sized forces and make precise measurements on a scale of roughly one micron. It can be created by applying a precisely focused laser through a microscope objective onto a dielectric material such as a cell or a Silica bead. It allows scientists to make very detailed manipulations and measurements on very small objects, and thus is a very important tool in biophysics. Optical traps are used in biological experiments ranging from cell sorting to the unzipping of DNA and also in physical applications such as atom cooling. In this experiment, you will calibrate the trap's position and force detection by trapping Silica beads and using the physics of Brownian motion. You will then use the apparatus to manipulate and study the motion of swimming E. coli cells and the transport of vesicles inside a living onion cell. http://advancedlab.org