AFM and XPS data sets for the influence of divalent cations on the adsorption and stability of DNA origami nanostructures at TiO2 surfaces

Substrate preparation: TiO2(110) wafers were purchased from CrysTec GmbH Kristalltechnologie. The substrates were immersed in a Hellmanex III solution (Hellma GmbH) for 2 h, followed by ultrasonication in ethanol and isopropanol for 5 min each. The substates were then thoroughly rinsed with HPLC-grade water (Carl Roth) and dried under a stream of argon. Subsequently, the cleaned substrates were treated with an O2 plasma (Zepto, Diener Electronic) for 1 minute. The substrates were subsequently characterized by AFM. If contaminants were observed in the AFM images, the cleaning procedure was repeated until a clean surface was obtained. DNA origami adsorption: DNA origami triangles were synthesized as described in DOI 10.1039/d5lf00109a, after which the folding buffer was exchanged against 1x TAE buffer supplemented with 10 mM MgCl2, CaCl2, or SrCl2 during spin filtration. The samples were diluted to a concentration of 2.5 nM with the respective buffer solutions. A 50 µL aliquot of each DNA origami sample was pipetted onto the TiO2(110) wafer and incubated for 10 min to allow adsorption. The substrate was then rinsed with HPLC-grade water and dried under a stream of argon. EDTA exposure: The TiO2(110) wafers with adsorbed DNA origami nanostructures were incubated for 30 s in TAE buffer solutions of varying concentrations of 0.01x, 0.02x, 0.05x and 0.1x, respectively. The substrates were subsequently rinsed with HPLC-grade water and dried under a stream of argon. AFM: Atomic force microscopy (AFM) images in the dry state of inteact and denatured DNA origami triangles adsorbed on TiO2(110) surfaces were recorded using either a Bruker Dimension Icon operated in ScanAsyst mode with SCANASYST-AIR cantilevers (Bruker), featuring a nominal tip radius of 2 nm, or a JPK NanoWizard 2 or 3 operated in intermittent contact mode with HQ/Al BS cantilevers (MikroMasch), featuring a nominal tip radius of < 8 nm. Images were acquired over a scan area of 2 x 2 µm2 with a resolution of 1024 x 1024 pixels. XPS: X-ray photoelectron spectroscopy (XPS) survey spectra were recorded for as-received and plasma-cleaned TiO2(110) wafers, as well as after 10 min exposure to 10 mM solutions of MgCl2, CaCl2, and SrCl2 in HPLC-grade water, respectively. This was done using an ESCA+ system (Omicron NanoTechnology) with a monochromatic Al Kα (1486.7 eV) X-ray source and a hemispherical energy analyzer in ultra-high vacuum. The base pressure of the machine was in the range of 10-10 mbar. The survey spectra were measured with a step size of 0.5 eV, a dwell time of 0.1 s and a pass energy of 100 eV. The take-off angle of the detected photoelectrons was 30° with respect to the surface plane while the source-analyzer angle was 102°. A low energy electron beam (1 eV) was used for neutralization.