Force dependence of the opening rate of a single DNA hairpin-loop

We directly measure the opening rate of a single DNA hairpin- loop (beacon) for different mechanical forces by optically monitoring the displacement of a $\mu $m sized bead tethered to a surface by a single DNA beacon (20 base pairs loop). We thus obtain a spectrum of rates, depending on mechanical forces (the range of 0-10pN), in contrast to FRET measurements which obtain only the zero force rate. In addition, our method gives access to long time scales.