Accurate position tracking of optically trapped live cells.

Niall McAlinden,Amanda J. Wright,David G. Glass,Owain R. Millington

doi:10.1364/boe.5.001026

Abstract

Optical trapping is a powerful tool in Life Science research and is becoming common place in many microscopy laboratories and facilities. There is a growing need to directly trap the cells of interest rather than introduce beads to the sample that can affect the fundamental biological functions of the sample and impact on the very properties the user wishes to observe and measure. However, instabilities while tracking large inhomogeneous objects, such as cells, can make tracking position, calibrating trap strength and making reliable measurements challenging. These instabilities often manifest themselves as cell roll or re-orientation and can occur as a result of viscous drag forces and thermal convection, as well as spontaneously due to Brownian forces. In this paper we discuss and mathematically model the cause of this roll and present several experimental approaches for tackling these issues, including using a novel beam profile consisting of three closely spaced traps and tracking a trapped object by analysing fluorescence images. The approaches presented here trap T cells which form part of the adaptive immune response system, but in principle can be applied to a wide range of samples where the size and inhomogeneous nature of the trapped object can hinder particle tracking experiments.

Highlights

Optical trapping is a well-established, well characterised technique that has been around for over thirty years and allows users to manipulate and control micron sized objects using a tightly focussed laser beam [1]
Many quantitative optical trapping experiments rely on manipulating beads that have been coupled to the target(s) of interest for the purpose of the experiment
We show how designing a multi-point optical trap can allow the cell as a whole to be trapped, rather than just a single feature, removing issues associated with cell roll and re-orientation

Summary

Introduction

Optical trapping (sometimes known as laser tweezers) is a well-established, well characterised technique that has been around for over thirty years and allows users to manipulate and control micron sized objects using a tightly focussed laser beam [1]. It has found application across the science disciplines and, in particular, is of growing demand in many fields of life science research. For small displacements from equilibrium position, x, an optical trap can be modelled as a harmonic potential,

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Discussion

Conclusion