Investigation of Cytoskeletal Systems with Optical Tweezers: Adhesion Forces of Actin Filaments and Malaria Parasites Measured with Optical Tweezers in Microfluidic Environments

Optical tweezers are a versatile tool to apply and measure forces in the piconewton range on microscopic objects that are held by optical forces in a focused laser beam. We employed holographic optical tweezers (HOT) to create extended force sensor arrays, consisting of multiple trapped particles that were controlled and probed individually. The combination of high-speed video microscopy with fluorescence imaging allowed the visualization of labeled protein structures in parallel with the tracking of multiple trapped particles for force measurements. Using this setup, we could perform quantitative force measurements on biological samples with HOT for the first time. This provided the possibility to measure dynamic processes such as the contractility of two-dimensional cross-linked actin networks in the microfluidic flow cell. To investigate bundling processes between filaments, a method has been established using dynamic HOT to manipulate zipper-like structures between trapped particles actively. In a different set of experiments, the adhesion process of the Malaria parasite Plasmodium was investigated. Using optical tweezers, the formation of adhesion sites was probed.