Nanomechanics of surface DNA switches probed by captive contact angle

Self-assembled monolayers of Thrombin Binding Aptamers (TBA) were prepared on gold surfaces with typical surface densities of close-packed ssDNA (4 × 1012 and 8 × 1012 molecules/cm2). CONtact Angle MOlecular REcognition (CONAMORE) in captive bubble geometry was then assessed to scan the surface work triggered by TBAs when switching from the elongated to the G-quadruplex conformation upon binding with Na+ or K+ cations. We found Na+ and K+ could induce comparable linear to G-quadruplex strokes, and resulted in values for surface work of ∼−70 pN nm/molecule (∼18 kBT). The strokes change the in-plane van der Waals and weak electrostatic interactions and accumulate to result in macroscopic surface work. Micro- to macroscopic translation strongly depends on the nature of the cation and TBA surface density. In particular, the K+ stimulus triggers a macroscopic surface work of −2.2 ± 0.2 and −5.3 ± 0.2 mN/m for low and high packed monolayers, respectively, while Na+ triggers up to −6.7 ± 1.0 mN/m in the highly packed monolayer, but creates negligible work for the low packed monolayer. These results show that CONAMORE can contribute important information for the development of devices based on DNA switches, and ultimately help address some of the open challenges for DNA-based nanomachinery.