Calibration of trapping force and response function of optical tweezers in viscoelastic media

Fischer, Mario; Berg-Sørensen, Kirstine

doi:10.1088/1464-4258/9/8/s18

Cited by 83 publications

(95 citation statements)

References 19 publications

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“…Using a recently developed in vivo calibration technique (Methods) (14,15), we measured the in vivo stall forces of lipid vesicles in A549 human epithelial cells and phagocytosed polystyrene beads in Dictyostelium discoideum. We used these two cell types to compare stall forces with each other.…”

Section: Resultsmentioning

confidence: 99%

In vivo optical trapping indicates kinesin’s stall force is reduced by dynein during intracellular transport

Blehm

Schroer

Trybus

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

106

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Kinesin and dynein are fundamental components of intracellular transport, but their interactions when simultaneously present on cargos are unknown. We built an optical trap that can be calibrated in vivo during data acquisition for each individual cargo to measure forces in living cells. Comparing directional stall forces in vivo and in vitro, we found evidence that cytoplasmic dynein is active during minus- and plus-end directed motion, whereas kinesin is only active in the plus direction. In vivo, we found outward (∼plus-end) stall forces range from 2 to 7 pN, which is significantly less than the 5- to 7-pN stall force measured in vitro for single kinesin molecules. In vitro measurements on beads with kinesin-1 and dynein bound revealed a similar distribution, implying that an interaction between opposite polarity motors causes this difference. Finally, inward (∼minus-end) stalls in vivo were 2–3 pN, which is higher than the 1.1-pN stall force of a single dynein, implying multiple active dynein.

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Section: Resultsmentioning

confidence: 99%

In vivo optical trapping indicates kinesin’s stall force is reduced by dynein during intracellular transport

Blehm

Schroer

Trybus

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

106

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“…13. In this section we provide a recipe of the practical implementation of the method and thus, we repeat only the essentials to ensure a consistent description.…”

Section: The Fdt Methodsmentioning

confidence: 99%

“…Simulation results and analytical considerations suggest that for a calibration, it is most practical and reliable to perturb the system with harmonic oscillations. 13 In the special case of a sinusoidally moved stage, x S ͑t͒ = A S sin͑ S t + S ͒, the trapped particle responds with sinusoidal motion, ͗x P ͑t͒͘ = A P sin͑ S t + P ͒. Equation ͑5͒ then becomes…”

Section: Fdt Methods Stage Driving Laser Drivingmentioning

confidence: 99%

“…In this paper we show how to apply the so-called fluctuation-dissipation theorem ͑FDT͒ method 13,14 to calibrate optical tweezers in a viscoelastic medium in a situation where the hydrodynamic interactions between the medium and the trapped particle are a priori unknown. The method combines passive and active measurements under conditions where the results of the FDT remain valid.…”

Section: Introductionmentioning

confidence: 99%

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Active-passive calibration of optical tweezers in viscoelastic media

Fischer

Richardson²,

Reihani

et al. 2010

Review of Scientific Instruments

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In order to use optical tweezers as a force measuring tool inside a viscoelastic medium such as the cytoplasm of a living cell, it is crucial to perform an exact force calibration within the complex medium. This is a nontrivial task, as many of the physical characteristics of the medium and probe, e.g., viscosity, elasticity, shape, and density, are often unknown. Here, we suggest how to calibrate single beam optical tweezers in a complex viscoelastic environment. At the same time, we determine viscoelastic characteristics such as friction retardation spectrum and elastic moduli of the medium. We apply and test a method suggested ͓M. Fischer and K. Berg-Sørensen, J. Opt. A, Pure Appl. Opt. 9, S239 ͑2007͔͒, a method which combines passive and active measurements. The method is demonstrated in a simple viscous medium, water, and in a solution of entangled F-actin without cross-linkers.

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“…3 Active methods are also important in instrument calibration: when working with viscoelastic media of unknown properties, such as the cytoplasm of a living cell, only by a combination of active and passive measurements can in situ force calibration of optical tweezers be performed. 4,5 Active calibration and viscosity measurements can also be used for purely viscous media, and optical trap calibration to a precision of 3% has been reported using an active phase-shift-based method. 6 To use active microrheology it is typically necessary to perform synchronized measurements of an external driving motion and the response of an optically trapped probe particle, in order to compare the two.…”

Section: Introductionmentioning

confidence: 99%

Multidepth, multiparticle tracking for active microrheology using a smart camera

Silburn

Saunter

Girkin

et al. 2011

Review of Scientific Instruments

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Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. The quantitative measurement of particle motion in optical tweezers is an important tool in the study of microrheology and can be used in a variety of scientific and industrial applications. Active microheology, in which the response of optically trapped particles to external driving forces is measured, is particularly useful in probing nonlinear viscoelastic behavior in complex fluids. Currently such experiments typically require independent measurements of the driving force and the trapped particle's response to be carefully synchronized, and therefore the experiments normally require analog equipment. In this paper we describe both a specialized camera and an imaging technique which make high-speed video microscopy a suitable tool for performing such measurements, without the need for separate measurement systems and synchronization. The use of a high-speed tracking camera based on a field programmable gate array to simultaneously track multiple particles is reported. By using this camera to simultaneously track one microsphere fixed to the wall of a driven sample chamber and another held in an optical trap, we demonstrate simultaneous optical measurement of the driving motion and the trapped probe particle response using a single instrument. Our technique is verified experimentally by active viscosity measurements on water-ethylene glycol mixtures using a phase-shift technique.

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Calibration of trapping force and response function of optical tweezers in viscoelastic media

Cited by 83 publications

References 19 publications

In vivo optical trapping indicates kinesin’s stall force is reduced by dynein during intracellular transport

In vivo optical trapping indicates kinesin’s stall force is reduced by dynein during intracellular transport

Active-passive calibration of optical tweezers in viscoelastic media

Multidepth, multiparticle tracking for active microrheology using a smart camera

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