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. 2015 Sep 3;44(1):e7. doi: 10.1093/nar/gkv866

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© The Author(s) 2015. Published by Oxford University Press on behalf of Nucleic Acids Research.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

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Figure 2. — Calibration of the DNA pulley. (A) Localization of a bead immobilized on a coverslip. A piezo stage displaced the sample in 5 nm steps. (B) Coordinate system for describing bead motion in the DNA pulley. The knife blade is on the left, and a DNA-tethered bead is stretched from the point of contact with the blade toward the magnet (not visible). The origin, O, is at the tip of the knife, the r-axis is along the direction of magnetic force, and the w-axis is orthogonal to the r-axis. (Inset) Thermal fluctuations of the tethered bead. The fluctuations were smaller along the r-axis (stretching the DNA) than along the w-axis (rotation about O). (C) Normalized autocorrelation functions of the bead displacement. Thermal fluctuations along the r-axis decayed faster than along the w-axis, as expected for the stiffer spring constant along the r-axis. Autocorrelation functions were calculated from 12 000 measurements acquired at 200 Hz.