The Stochastic Force Spectrum of a Micro-Swimmer

We seek to understand the dynamics of micro-swimmers by quantifying the stochastic forces generated by their motion. We are currently working with Chlamydomonas Reinhardtii—a green algae commonly used to study microscopic locomotion. Our approach is to use optical tweezers and a direct force calibration known as the photon momentum method (PMM) to measure micro-swimmer forces. The power spectral density (PSD) of the force dynamics is analyzed, providing information about the frequency content of the force signals. A simple stochastic model based on the generalized Langevin equation predicts the power spectral density to have a Lorentzian-type curvature. We compare our experimental data to the theoretical model to test if the model can predict our experimentally measured PSD. This approach allows the calculation of thermodynamic quantities such as work, power, efficiency, etc. to describe the microscopic motion. Our analysis seeks to apply concepts from stochastic thermodynamics to understand micro-swimmer dynamics.