FM-AFM constant height imaging and force curves: high resolution study of DNA-tip interactions

Area of Science:

• Nanoscience
• Biophysics
• Materials Science

Background:

• Atomic Force Microscopy (AFM) can invasively interact with soft samples.
• Frequency Modulation AFM (FM-AFM) enables non-contact scanning, minimizing sample damage.
• Previous studies successfully used FM-AFM for atomic resolution of non-biological molecules.

Purpose of the Study:

• To investigate the application of FM-AFM for studying biological samples, specifically double-stranded DNA (dsDNA).
• To achieve high-resolution imaging of dsDNA adsorbed on a modified mica substrate in ultra-high vacuum.
• To explore the behavior of dehydrated and adsorbed DNA under non-contact AFM conditions.

Main Methods:

• Experiments were conducted using FM-AFM on dsDNA deposited on 3-aminopropyltriethoxysilane modified mica in ultra-high vacuum.
• Non-contact topographic imaging was employed to capture DNA surface variations.
• Frequency shift maps and distance curves were acquired to analyze tip-sample interactions and forces.

Main Results:

• Non-contact topographic images revealed variations with the periodicity of right-handed B-form DNA, contrary to expectations for dehydrated DNA (A-form).
• Frequency shift maps provided rich contrast and resolved 0.2 to 0.4 nm details on DNA.
• Force curves indicated substrate contributions to the interaction force for DNA molecules under 2.5 nm height.

Conclusions:

• FM-AFM provides a gentle and high-resolution method for imaging dehydrated and adsorbed DNA.
• The study presents unexpected findings on DNA structure and interaction forces, suggesting longer tip-sample interaction distances.
• These results have potential implications for DNA-based nanotechnology, including nanoelectronics and nanotemplating in non-physiological environments.