Optical Tweezer Experiments

Quantifying and Pinpointing Sources of Noise

Dec. 18, 2009

Optical trapping techniques have evolved to the point where quantitative force measurements on biological systems can be performed down into the femtonewton range. As resolution is constantly improving, the pinpointing and elimination of noise sources become increasingly important. Allan-variance analysis is ideally suited for this task; adjacent time series are recorded and the variations between observation intervals are calculated.

Here, we provide a comprehensive toolbox consisting of: a reliable data-streaming acquisition software that allows for streaming long adjacent time series (~30min), even with high sampling frequencies (>80kHz); an analysis software (Matlab-based) with calculation times of only a few seconds; and fitting scripts to extract parameters of noise and drift sources. Furthermore, the validity and robustness of Allan-variance analysis is demonstrated in data obtained from our optical-tweezers setup wherein laboratory-specific noise sources are detected. In addition, a detailed Allan-variance analysis clarifies the difference between two common detection systems, a quadrant photodiode and a position-sensitive photodiode.

Lastly, we demonstrate how our toolbox can be applied to position-time traces of optically trapped spheres to determine the optimal calibration interval for any setup, suitable settings for variance and update rates in force-feedback loops, and variations due to the geometrical constraints of the sample chamber. Allan-variance analysis can be used as a standard tool enabling reliable comparison of different optical-tweezers setups and the precise quantification of noise and drift sources, which are particularly relevant in high precision experiments with individual biomolecules.

This poster was presented at NanoBioViews 2009; 14-15 October 2009: http://www.nanobioviews.net

Contact:
Fabian Czerwinski
Optical Tweezers Group
Niels Bohr Institute
Blegdamsvej 17
2100 Copenhagen, Denmark
czerwinski@nbi.dk

Authors:
Fabian Czerwinski
Ulrich F. Keyser
Lene B. Oddershede

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Quantifying and Pinpointing Sources of Noise

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