Fig. S1.
Instrumental response time. (A) The response time of the optical tweezers to changes in extension, tc, was measured using a reference construct consisting of DNA handles only. The construct was held at about 10, 14, and 19 pN, and one trap was jumped abruptly back and forth to cause the extension to change by an amount equivalent to the extension change in the folding of the hairpins. (B) Extension trajectories of the handle-only reference construct (black) were analyzed in the same way as the folding/unfolding transitions, measuring tc from individual transitions (red) as the time required to move between the boundaries x1 and x2 (dotted lines). Back-and-forth motion in the trajectories reflects the diffusive motion of the bead. (C) The distribution of response times was peaked near 4–6 μs for the different forces, with an average of 6 ± 1 (20 pN) to 9 ± 1 (10 pN) μs.