Practical axial optical trapping

We describe a new method for calibrating optical trapping measurements in which tension is applied in the direction of the laser beam to a molecule tethered between a surface and an optically trapped bead. Specifically, we present a generally-applicable procedure for converting from the measured sca...

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Bibliographic Details
Published in:Review of scientific instruments 2012-10, Vol.83 (10), p.103106-103106
Main Authors: Mack, A H, Schlingman, D J, Regan, L, Mochrie, S G J
Format: Article
Language:English
Subjects:
Beads
Beams (radiation)
Biomechanical Phenomena
Calibration
Deoxyribonucleic acid
Displacement
DNA - chemistry
DNA - metabolism
Laser beams
Lasers
Optical trapping
Optical Tweezers
Optics
Atoms and Molecules
Spectroscopy
Photon Detectors
Scattering, Radiation
Signal Processing, Computer-Assisted
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Summary:We describe a new method for calibrating optical trapping measurements in which tension is applied in the direction of the laser beam to a molecule tethered between a surface and an optically trapped bead. Specifically, we present a generally-applicable procedure for converting from the measured scattering intensity and the measured stage displacement to applied tension and bead-coverslip separation, using measurements of the light intensity scattered from an untethered, trapped bead. Our calibration accounts for a number of effects, including aberrations and the interference of forward-reflected bead-scattered light with the trapping beam. To demonstrate the accuracy of our method, we show measurements of the DNA force-versus-extension relation using a range of laser intensities, and show that these measurements match the expected extensible wormlike-chain (WLC) behavior. Finally, we also demonstrate a force-clamp, in which the tension in a tether is held fixed while the extension varies as a result of molecular events.
ISSN:0034-6748
1089-7623
DOI:10.1063/1.4757862