Abstract
We present a new method for calibrating an optical-tweezer setup that does not depend on input parameters and is less affected by systematic errors like drift of the setup. It is based on an inference approach that uses Bayesian probability to infer the diffusion coefficient and the potential felt by a bead trapped in an optical or magnetic trap. It exploits a much larger amount of the information stored in the recorded bead trajectory than standard calibration approaches. We demonstrate that this method outperforms the equipartition method and the power-spectrum method in input information required (bead radius and trajectory length) and in output accuracy.
Highlights
Optical tweezers, first constructed and used by Arthur Ashkin during the 1970s and 1980s [1], are widely used for single molecule manipulation [2]
Transmitted light was collected with a high numerical aperture condenser (Olympus Aplanat Achromat, NA = 1.4) and directed to a quadrant photodiode (QPD) (SPOT-9DMI, OSI Optoelectronics) located in a plane conjugated with the back focal plane (BFP) of the microscope objective
Bayesian inference analysis of the recorded bead trajectories does not depend on external drift and does not require any input parameters
Summary
First constructed and used by Arthur Ashkin during the 1970s and 1980s [1], are widely used for single molecule manipulation [2]. Its effective spring constant needs to be determined to relate the bead displacement within the trap to the corresponding force experienced by the bead To this end, a variety of methods have been developed using the same beam as the optical trapping beam to record the bead trajectory inside the trap and extract the trap stiffness from it. Two-beam approaches have been introduced using one laser beam to trap the bead and a second low-power one to measure its displacement inside the trap [23]. This configuration is more complicated to implement and to align but is interesting for cases where the absolute bead location has to be known or for multiple-trap experiments
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