Microrheology with an anisotropic optical trap

Matheson, A. B., Mendonca, T., Gibson, G. M. , Dalgarno, P. A., Wright, A. J., Paterson, L. and Tassieri, M. (2021) Microrheology with an anisotropic optical trap. Frontiers in Physics, 9, 621512. (doi: 10.3389/fphy.2021.621512)

Abstract

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 analysed in future applications.

• Item Type: Articles
• Additional Information: We acknowledge support via EPSRC grant Experiencing the micro-world - a cell’s perspective (EP/R035067/1 – EP/R035563/1– EP/R035156/1).
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Gibson, Dr Graham and Tassieri, Dr Manlio
• Authors: Matheson, A. B., Mendonca, T., Gibson, G. M., Dalgarno, P. A., Wright, A. J., Paterson, L., and Tassieri, M.
• College/School: College of Science and Engineering > School of Engineering > Biomedical Engineering; College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Frontiers in Physics
• Publisher: Frontiers Media
• ISSN: 2296-424X
• ISSN (Online): 2296-424X
• Copyright Holders: Copyright © 2021 The Authors
• First Published: First published in Frontiers in Physics 9:621512
• Publisher Policy: Reproduced under a Creative Commons License

Project Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
301441		Experiencing the micro-world - a cell's perspective	Manlio Tassieri	Engineering and Physical Sciences Research Council (EPSRC)	EP/R035067/1	ENG - Biomedical Engineering