AFM imaging and analysis of electrostatic double layer forces on single DNA molecules

Area of Science:

• Biophysics
• Surface Science
• Nanotechnology

Background:

• Electrical double layer (EDL) forces are crucial at interfaces between charged surfaces and electrolyte solutions, particularly in biological systems.
• DNA molecules, as standard single biomolecules, are ideal for studying nanoscale forces in physiological environments.

Purpose of the Study:

• To investigate and visualize the electrical double layer (EDL) forces exerted by DNA molecules on a substrate.
• To develop and apply a method for resolving EDL forces using atomic force microscopy (AFM).

Main Methods:

• Utilized atomic force microscope (AFM) in force spectroscopy imaging mode to characterize DNA molecules on substrates.
• Employed linear superposition to account for both tip-substrate and tip-molecule interactions in EDL force analysis.
• Generated EDL force images to visualize DNA molecules and their associated forces.

Main Results:

• Successfully resolved DNA molecules in EDL force images, demonstrating the method's effectiveness.
• Compared the lateral resolution of EDL force imaging with topographic imaging.
• Estimated the surface charge density of DNA, yielding reasonable values.

Conclusions:

• AFM force spectroscopy imaging is a viable technique for visualizing EDL forces from single DNA molecules.
• The developed method allows for the characterization of nanoscale forces and estimation of biomolecular surface charge.
• This approach advances the understanding of electrostatic interactions involving DNA in solution.