Omcl ac200ts c2

For AFM imaging using an SPM-9700 (Shimadzu, Kyoto, Japan), 0.3 μM plasmid DNA (4331 bp) was dissolved in 10 mM Tris-HCl buffer solution at pH 7.5 with various concentrations of polyamines. The DNA solution was incubated for more than 10 min and then transferred onto a freshly cleaved mica surface. Subsequently, the sample was rinsed with ultra-pure water, dried with nitrogen gas and imaged by AFM. All measurements were performed in air using the tapping mode. The cantilever, OMCL-AC200TS-C2 (Olympus, Tokyo, Japan), was 200 μm long with a spring constant of 9–20 N/m. The scanning rate was 0.4 Hz and images were captured using the height mode in a 512 × 512 pixel format. The obtained images were plane-fitted and flattened by the computer program supplied with the imaging module.

For AFM imaging using an SPM-9700 (Shimadzu, Kyoto, Japan), 0.3 μM plasmid DNA was dissolved in 10 mM Tris-HCl buffer solution (pH 7.5) with various concentrations of polyamines. The DNA solution was incubated for 10–15 minutes and then transferred onto a freshly cleaved mica surface. The mica surface was not pretreated with any cationic species. After it was allowed to stand for 10 min at room temperature (25°C), the mica was rinsed with water and dried under nitrogen gas. All measurements were performed in air using the tapping mode. The cantilever (OMCL-AC200TS-C2, Olympus, Tokyo, Japan) was 200 μm long with a spring constant of 9–20 N/m. The scanning rate was 0.4 Hz and images were captured using the tapping mode in a 256 × 256 or 512 × 512 pixel format. The obtained images were plane-fitted and flattened by the computer program supplied with the imaging module. An AFM image of DNA at a low concentration of 0.004 mM SPD(3+) or 0.004 mM SP(4+) was used as a control.