Laser polarization driven micromanipulation and reorientation dynamics of an asymmetric shaped microscopic biomaterial using optical tweezers

Abstract

We present measurements and a theoretical model that describes the dynamics of ellipsoidal shaped, chicken red blood cells (cRBCs) reorienting in an optical trap and demonstrates the ability to control their reorientation through changes in the intensity distribution that results from the different states of the polarization of the trapping laser. We have observed that in linearly polarized light, cRBC, a type of avian RBC, undergoes dual reorientation, with the first reorientation about the cell’s major axis and the second, about its short minor axis, with the major axis aligning with the laser propagation direction at equilibrium. We compute the work done for each of these reorientations and attribute the observed dynamics to a minimization of the energy cost for the particular sequence of the reorientations that we observe. Further, we achieve a controlled second orientation of the major axis along the laser propagation direction by varying the ellipticity of the polarization of the laser. We explain these partial second reorientation results by employing a geometrical optics-based model. Characterizing the dynamics and control of these regular-shaped natural soft materials through optical polarization is relevant in the context of current work in the design and development of microscopic artefacts such as lab-on-a-chip platforms.