Imaging stretched single DNA molecules by pulsed-force-mode atomic force microscopy.

Area of Science:

• Biophysics
• Materials Science
• Nanotechnology

Background:

• Studying DNA conformation and interactions on surfaces is crucial for nanotechnology and molecular biology.
• Atomic force microscopy (AFM) offers high-resolution imaging but can be limited by environmental conditions, especially aqueous solutions.

Purpose of the Study:

• To investigate the effect of a surface water layer on DNA strands deposited on a substrate.
• To evaluate the efficacy of pulsed-force-mode AFM (PFM-AFM) for imaging stretched DNA in aqueous environments.

Main Methods:

• DNA molecules (Lambda bacteriophage) were stretched and aligned on organosilane-modified glass coverslips using molecular combing.
• Imaging was performed using pulsed-force-mode AFM (PFM-AFM) in both humidity-controlled air and aqueous solutions.
• Cantilevers were chemically modified with organothiol compounds for enhanced DNA observation.

Main Results:

• PFM-AFM successfully imaged stretched DNA molecules on silane-modified substrates in aqueous solutions.
• Mapping adhesive forces in aqueous media allowed for chemical discrimination between DNA strands and the substrate.
• The study demonstrated the capability of PFM-AFM to visualize DNA under varying humidity and in liquid environments.

Conclusions:

• PFM-AFM is a versatile technique for imaging stretched DNA on silane-modified substrates, even in the presence of a surface water layer.
• The method allows for detailed analysis of DNA conformation and surface interactions in biologically relevant aqueous conditions.
• This technique holds promise for broader applications in nanoscale biological imaging and analysis.