Designing an experiment to measure cellular interaction forces

Niall McAlinden, David Gavin Glass, Owain Millington, Amanda Wright

Research output: Chapter in Book/Report/Conference proceedingConference contribution book

1 Citation (Scopus)


Optical trapping is a powerful tool in Life Science research and is becoming common place in many microscopy laboratories and facilities. The force applied by the laser beam on the trapped object can be accurately determined allowing any external forces acting on the trapped object to be deduced. We aim to design a series of experiments that use an optical trap to measure and quantify the interaction force between immune cells. In order to cause minimum perturbation to the sample we plan to directly trap T cells and remove the need to introduce exogenous beads to the sample. This poses a series of challenges and raises questions that need to be answered in order to design a set of effect end-point experiments. A typical cell is large compared to the beads normally trapped and highly non-uniform – can we reliably trap such objects and prevent them from rolling and re-orientating? In this paper we show how a spatial light modulator can produce a triple-spot trap, as opposed to a single-spot trap, giving complete control over the object’s orientation and preventing it from rolling due, for example, to Brownian motion. To use an optical trap as a force transducer to measure an external force you must first have a reliably calibrated system. The optical trapping force is typically measured using either the theory of equipartition and observing the Brownian motion of the trapped object or using an escape force method, e.g. the viscous drag force method. In this paper we examine the relationship between force and displacement, as well as measuring the maximum displacement from equilibrium position before an object falls out of the trap, hence determining the conditions under which the different calibration methods should be applied.
Original languageEnglish
Title of host publicationSPIE Proceedings
Subtitle of host publicationusing the photonic toolbox to study cells and their organelles
EditorsKishan Dholakia, Gabriel C. Spalding
Place of PublicationBellingham
Publication statusPublished - 2013
EventProc. SPIE 8810, Optical Trapping and Optical Micromanipulation X - San Diego, United Kingdom
Duration: 25 Aug 2013 → …


ConferenceProc. SPIE 8810, Optical Trapping and Optical Micromanipulation X
Country/TerritoryUnited Kingdom
CitySan Diego
Period25/08/13 → …


  • calibration
  • transducers
  • lasers
  • optical trapping
  • spatial light modulator

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