Figure 1.

Schematic of the setup. (a) Counterpropagating optical trap with a light-momentum force sensor modified to include a temperature controller. The heating beam passes through a 45° dichroic long-pass filter (Edmund Optics 69-878), which acts as a cold mirror, thus reflecting the blue LED light, which illuminates the experiment, until a CCD camera and allowing the heating wavelength to pass through. (b) Single-molecule experiment. The DNA hairpin under study is attached between two polystyrene beads: one captured in the optical trap and the other held by air suction on the tip of a micropipette (see text for details). To see this figure in color, go online.