Time-shared optical tweezers for active microrheology inside cells

Abstract

The use of non-invasive, optical tweezers active microrheology provides invaluable information on the mechanobiological principles that govern most cellular processes. The principle of using a single laser beam to trap —either endogenous droplets or microinjected probe beads— and measure both the displacement and the force during an imposed oscillation has been proven insufficient for obtaining the response function, ˆχ(ω), and the G modulus, ˆG(ω). As a solution, an additional laser with very low power can be used to measure probe displacements independently, to the detriment of the simplicity of the optical trapping set-up, robustness and cost. Here, we present a method to carry out position and force measurements with a single trapping beam through the time-sharing mode of an optical micromanipulation unit modulated with acousto-optic deflectors.