A magnetic viscometer for shear-sensitive macromolecules

Area of Science:

• Biophysics
• Rheology
• Macromolecular Science

Background:

• Accurate viscosity measurements are crucial for understanding biological macromolecules.
• Traditional viscometers face challenges with surface disturbances and sample handling.
• Characterizing DNA and chromatin viscosity requires specialized techniques.

Purpose of the Study:

• To develop and report on a novel rotation-viscometer for biological macromolecules.
• To overcome limitations of existing viscometry methods, such as surface disturbance.
• To accurately measure the intrinsic viscosity of DNA and the rheological properties of chromatin.

Main Methods:

• A rotation-viscometer with a submerged rotor was designed and implemented.
• Electromagnetic suspension and light barriers were used for rotor control and centering.
• A rotating electromagnetic field drove the rotor, with revolution periods measured electronically.
• Low rotor speeds minimized shearing effects for intrinsic viscosity determination.

Main Results:

• The viscometer effectively measures viscosity of biological macromolecules, avoiding surface disturbance.
• Intrinsic viscosity values for DNA were obtained by extrapolating concentration dependence at low shear rates.
• Chromatin exhibited very low viscosity with minimal concentration dependence.
• Decreasing ionic strength of chromatin solutions led to increased viscosity, indicating structural unfolding.

Conclusions:

• The developed rotation-viscometer is suitable for precise viscosity measurements of biological macromolecules like DNA and chromatin.
• The device allows for accurate determination of DNA intrinsic viscosity.
• Chromatin's rheological behavior is sensitive to ionic strength, reflecting structural changes.