Fig. 8. Reversible control of protein activity using DNA tweezers. Two double-crossover motifs are joined via a Holliday junction. The addition of a fuel strand, complementary to an internal stem-loop structure, induces the opening of the tweezer. Consequently, the distance between the tips is increased. Functionalization of the tips with specific aptamers allows switching between mono- and bivalent thrombin binding, reversibly releasing and capturing thrombin, respectively (reprinted with permission from ref. 51, copyright 2012, American Chemical Society).