Electrostatic force microscopy: imaging DNA and protein polarizations one by one

Area of Science:

• Molecular Biophysics
• Surface Science
• Nanotechnology

Background:

• Understanding the electrostatic properties of biological molecules like DNA and transcription complexes is crucial for molecular interactions and function.
• Imaging these properties at the molecular level on insulating substrates presents significant technical challenges.

Purpose of the Study:

• To image and quantify the electrostatic properties of double-stranded DNA and transcription complexes at molecular resolution on an insulating substrate.
• To determine the dipole moments and electric polarizability of individual DNA and transcription complexes.

Main Methods:

• Utilizing frequency-mode noncontact atomic force microscopy (NC-AFM) to obtain electrostatic force microscopy (EFM) images.
• Employing scanning capacitance microscopy (SCM) to assess electric polarizability differences.

Main Results:

• EFM images revealed molecular polarization with an upward dipole moment for both DNA and transcription complexes.
• Estimated dipole moments were 0.027 D/base for DNA and 0.16 D/molecule for the transcription complex.
• SCM showed contrast inversion, indicating distinct electric polarizability between DNA and transcription complexes.

Conclusions:

• Individual biological molecules' electrostatic properties can be imaged on insulating substrates while preserving complex formation.
• The study provides quantitative insights into the dipole moments and polarizability of DNA and transcription complexes.
• These findings open avenues for understanding molecular interactions governed by electrostatic forces in biological systems.