Microrheology With an Anisotropic Optical Trap

Frontiers in Physics

Manlio Tassieri¹  Amanda J. Wright²  Tania Mendonca²  Andrew B. Matheson³  Paul A. Dalgarno³  Lynn Paterson³  Graham M. Gibson⁴ 

[1] Division of Biomedical Engineering, James Watt School of Engineering, University of Glasgow, Glasgow, United Kingdom;Optics and Photonics Research Group, Faculty of Engineering, University of Nottingham, Nottingham, United Kingdom;School of Engineering and Physical Sciences, Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot Watt University, Edinburgh, United Kingdom;School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom;

关键词: microrheology;    optical trapping;    anisotropy;    optical tweezers;    simulations;   

DOI  :  10.3389/fphy.2021.621512

来源: Frontiers

【 摘 要 】

Microrheology with optical tweezers (MOT) measurements are usually performed using optical traps that are close to isotropic across the plane being imaged, but little is known about what happens when this is not the case. In this work, we investigate the effect of anisotropic optical traps on microrheology measurements. This is an interesting problem from a fundamental physics perspective, but it also has practical ramifications because in 3D all optical traps are anisotropic due to the difference in the intensity distribution of the trapping laser along axes parallel and perpendicular to the direction of beam propagation. We find that attempting viscosity measurements with highly anisotropic optical traps will return spurious results, unless the axis with maximum variance in bead position is identified. However, for anisotropic traps with two axes of symmetry such as traps with an elliptical cross section, the analytical approach introduced in this work allows us to explore a wider range of time scales than those accessible with symmetric traps. We have also identified a threshold level of anisotropy in optical trap strength of ~30%, below which conventional methods using a single arbitrary axis can still be used to extract valuable microrheological results. We envisage that the outcomes of this study will have important practical ramifications on how all MOT measurements should be conducted and analyzed in future applications.

【 授权许可】

CC BY