Constructing an optical tweezers instrumentation and evaluation of trapping stiffness using the power spectrum method

Sammanfattning

Optical tweezers can trap micron-sized objects such as cells, bacteria, and microspheres, and has become an important instrument for measuring forces associated with various physical and biological phenomena. In this thesis work, I constructed an optical tweezers instrument to trap 2µm diameter beads using a HeNe-laser operating with a wavelength of 632.8nm. Trapped beads were imaged using a charge-coupled device (CCD) camera. Since quantitative use of optical tweezers relies on the precise calibration of the trapping stiffness, I used a position sensitive detector (PSD) to measure the Brownian motion of trapped beads. The lateral stiffness of the optical tweezers was evaluated by fitting a Lorentzian to the power spectrum of the Brownian motion of the trapped 2µm beads, which were found to be 6.4(2)pN/µm in the x-direction and 6.0(1)pN/µm in the y-direction. Thus, I realized an optical tweezers setup that could trap and measure the position of micron-sided particles and I developed algorithms to calibrate the stiffness of the trap.