Ac160ts cantilever

All AFM images were collected using the RIBM HS-AFM 1.0 instrument. The AFM measurements were performed in the tapping mode using Olympus AC 160 TS cantilevers; the resonant frequency and the spring constant of the cantilevers were 300 kHz and 42 N/m, respectively, and the tip’s radius was 9±2 nm. Measurements in solution were performed in a liquid flow cell. AFM images were processed using the plane subtraction and row alignment by a median of differences methods within the Gwyddion package.⁵¹ Prior to each measurement, all HOPG samples were freshly cleaved using the scotch tape method.^{32 (link)} In the case of AFM imaging in air, a 1 μl droplet of buffer solution was placed on top of the HOPG sample. The sample was incubated for 10 minutes, rinsed with DI water and blowdried with nitrogen gas. For AFM imaging in solution, the buffer solution was introduced into the liquid flow cell; the flow cell was placed on top of the freshly cleaved HOPG surface. The buffer solution containing 1 M KCl and 1 mM EDTA was prepared by mixing stock solutions of KCl and EDTA. The M13 DNA sample was first heated to 95 C, kept at that temperature for 20 minutes and then rapidly cooled on ice. The final sample was prepared by mixing DNA with the 1 KCl/1 mM EDTA buffer to achieve 0.1 ng/μl concentration of DNA.