DNA as a metrology standard for length and force measurements with optical tweezers - PubMed (original) (raw)

DNA as a metrology standard for length and force measurements with optical tweezers

John Peter Rickgauer et al. Biophys J. 2006.

Abstract

Optical tweezers have broad applications in studies of structures and processes in molecular and cellular biophysics. Use of optical tweezers for quantitative molecular-scale measurement requires careful calibration in physical units. Here we show that DNA molecules may be used as metrology standards for force and length measurements. Analysis of DNA molecules of two specific lengths allows simultaneous determination of all essential measurement parameters. We validate this biological-calibration method experimentally and with simulated data, and show that precisions in determining length scale factor ( approximately 0.2%), length offset ( approximately 0.03%), force scale factor ( approximately 2%), and compliance of the traps ( approximately 3%) are limited only by current measurement variation, much of which arises from polydispersity of the microspheres ( approximately 2%). We find this procedure to be simpler and more convenient than previous methods, and suggest that it provides an easily replicated standard that can insure uniformity of measurements made in different laboratories.

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Figures

FIGURE 1

Experimental geometry. The distance between the two optical traps is d, the end-to-end extension of the tethered DNA is x, the radii of the trapped microspheres are _r_1 and _r_2, the force on the microspheres is F, and the displacements of the microspheres from the trap centers are Δ_x_1 and Δ_x_2.

FIGURE 2

Averaged experimental datasets recorded for DNA molecules of the indicated lengths (points) and fits to Eq. 7 (solid lines, overlaid). Deviations from the fits are shown in the two lower plots. The fits were used to determine the measurement parameters listed in Table 1.

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DNA as a metrology standard for length and force measurements with optical tweezers - PubMed (original) (raw)