AFM images of DNA origami adsorption and lattice assembly on SiO2 surfaces under electrochemical control

In-situ AFM images of DNA origami triangles adsorbed on Si(100) wafers (p-doped, 1 – 10 Ωcm) with hydroxylated surface oxide under electrochemical control. AFM measurements were performed using a JPK Nanowizard ULTRA Speed with USC F0.3-k0.3 cantilevers (NanoWorld) and an electrochemical cell (1.5 ml cell volume, JPK). A three-electrode setup was employed, comprising the bare silicon wafer with native oxide contacted from the backside as the working electrode, a platinum wire as the counter electrode, and a platinum wire as the pseudo-reference electrode. This setup was connected to a Gamry Femtostat FAS12 to apply the substrate potentials. The open circuit potential (OCP) of the substrate in DNA-free electrolyte was recorded before introducing the sample solution. After sample injection, a selected potential vs. OCP was applied to the substrate in chronoamperometry mode. For dataset "potential screening", 0.5 nM DNA origami triangles in 1xTAE (pH 8.5) containing 12.5 mM CaCl₂ and 400 mM NaCl were incubated for 10 to 15 min at different potentials ranging from -50 to -250 mV to evaluate their adsorption and mobility on the surface. For dataset "lattice assembly - potential dependence", 4 nM DNA origami triangles in 1xTAE (pH 8.5) containing 12.5 mM CaCl₂ and 400 mM NaCl were incubated for up to 120 min at different potentials ranging from -100 to -170 mV. AFM images were recorded at regular intervals to monitor DNA origami lattice assembly. For dataset "lattice assembly - concentration dependence", 4 nM DNA origami triangles in 1xTAE (pH 8.5) containing different concentrations of CaCl₂ and NaCl were incubated at -120 mV. AFM images were recorded after about 120 min incubation.