Molecular imaging picoplus 2500 afm

The structures of the surfactant/ctDNA complexes were investigated using AFM. A Molecular Imaging PicoPlus 2500 AFM (Agilent Technologies, Santa Clara, CA, USA) was used. A resonance frequency of around 240 KHz and a nominal force constant of 42 N/m were the working conditions, using silicon cantilevers (Model Pointprobe, Nanoworld, Neufchâtel, Switzerland). The images were recorded in air and in tapping mode. Data collection was registered at 256 × 256 pixels, with scan speeds about 0.5 Hz. The ctDNA concentration was 0.6 μM, keeping pH = 7.4 (HEPES 10 mM).
Images of surfactant/ctDNA buffered solutions were obtained using the following method. (i) 0.1% (v/v) APTES aqueous solution was dropped onto a freshly cleaved mica surface in order to prepare a modified mica surface. After 20 min, it was washed with ultra-pure water and air dried. (ii) A 30 μL droplet of the surfactant/ctDNA buffered solution was deposited on the modified mica surface and incubated for 30 min. (iii) Afterwards, it was washed with pure water and air dried for AFM imaging.

Atomic force microscopy was used to study the structures of the lipoplexes. A resonance frequency of around 240 KHz and a nominal force constant of 42 N/m were the working conditions in a Molecular Imaging PicoPlus 2500 AFM (Agilent Technologies, Santa Clara, CA, USA). Silicon cantilevers (Model Pointprobe, Nanoworld, Neufchâtel, Switzerland) were used. The images were recorded in air and in tapping mode. Data collection (256 × 256 pixels) was registered with scan speeds about 0.5 Hz. The ctDNA concentration in the buffered HEPES 10 mM liposome solutions, pH = 7.4, was 0.6 μM.
Images of the buffered liposome solutions were obtained using the following method: (a) In order to prepare a modified mica surface, 0.1% (v/v) APTES aqueous solution was dropped onto a freshly cleaved mica surface. It was washed with ultra-pure water after 20 min and air dried. (b) A 30 μL droplet of the lipoplex solution was deposited on the modified mica surface and incubated for 30 min. (c) Subsequently, the mica surface was washed with pure water and air dried for AFM imaging.