Micro cantilever

AFM images were obtained using micro cantilever (OLYMPUS, Tokyo, Japan) and the dynamic force mode with Probestation NanoNavi II/IIe (Hitachi High-Tech Science, Tokyo, Japan). Five to twenty microliters of a sample were loaded to a mica plate, left for one minute, and then rinsed using 200 μL of water. The sweep rate was set to 0.5 or 1.0 Hz.

Langmuir-Blodgett studies was carried out for compound C14, being the ultimate compound with both surface active and antioxidant properties, according to the method of Correa et al.^{29 (link)} with slight modications. Experiments were performed in aqueous solutions at neutral pH. Briefly, 20 µl of 2 mg/mL solution of C14 in chloroform:methanol (9:1, v/v) was applied to the aqueous phase and allowed to evaporate for a period of 20 min. Thereafter, the barriers were compressed at a constant rate of ~9 Å/ (chain min) until film collapsed. After stable conditions were attained, deposition of the corresponding film was carried out onto a hydrophilic mica support at a pressure just before film collapsed. The deposited monolayers on mica were left to air dry overnight. AFM images were acquired at ambient conditions by air tapping mode using a silicon tip on a micro cantilever (Olympus Inc., Japan) with a spring constant of 26 N/m and resonant frequency of 300 kHz. All measurements were performed in the center of the sample. Analyses were done in duplicates.

The ring motif and its self-assembly were monitored by high speed atomic force microscopy (AFM) (Nano Live Vision, RIBM, Kyoto, Japan) with Micro Cantilevers (Olympus, Tokyo, Japan). Each measurement was performed in a liquid cell in an observation buffer (5 mM Tris, 1 mM EDTA, and 12.5 or 17.5 mM MgCl₂). The concentration of the motif was constantly maintained at 1 nM. The substrate for AFM observation was a freshly cleaved mica (Furuuchi Chemical Corporation, Tokyo, Japan). Images were recorded with 1500 × 1125 nm² scan size. The observation was conducted about 10 min after injection of the unpurified DNA origami solution. The images were analyzed using ImageJ open-source software.