Fig. 1: Design of a dual-switching nanospring.

a Reversible transformation of a DNA origami bundle into a spring shape through the cumulative actuation of K⁺-responsive modules. The details of the module (dashed red box) are shown in b and Supplementary Fig. 2. b Schematics of the module. The ssDNA bridge strand containing a G-rich sequence (5′-GGGTTAGGGTTAGGGTTAGGG-3′) flanked with staple sequences is incorporated in the module. The strand forms a G-quadruplex in the presence of K⁺, which leads to the bending of the module. The strand can also hybridize with an anti-GQ strand carrying a toehold sequence (5′-CCCTAACCCTAACCCTAACCCAGAGAACT-3′). The 21 bp duplex induces bending whose direction is opposite to that induced by the GQ-formation. The anti-GQ strand can be displaced from the module via the toehold-mediated strand displacement process with a releaser strand, 5′-AGTTCTCTGGGTTAGGGTTAGGGTTAGGG-3′, whose sequence is fully complementary to the anti-GQ strand. c Representative AFM images of the nanosprings of over three independent experiments taken after the hybridization with the anti-GQ strand, in the absence of both the anti-GQ strand and 100 mM KCl, and in the presence of 100 mM KCl. Inset scale bar is 50 nm. d, e Histograms of the curvature radius of the nanospring after hybridization with anti-GQ strands d and that in the presence of 100 mM KCl without bound anti-GQ e. n represents the total number of nanospring molecules evaluated. f, g Number of turns calculated from the curvature radius and number of turns for nanospring measured by AFM after hybridization with anti-GQ strands f and that in presence of 100 mM KCl without bound anti-GQ g. The errors refer to standard deviations (SD). Source data are provided as a Source Data file.