Protein dielectrophoresis: Key dielectric parameters and evolving theory

Area of Science:

• Biophysics
• Dielectrics
• Protein Science

Background:

• Standard dielectrophoresis (DEP) theory struggles to explain experimental observations for globular proteins.
• The applied field gradient factor is often insufficient to overcome thermal energy (kT) and protein dispersive forces.

Purpose of the Study:

• To propose a new DEP force equation that accurately describes protein behavior in electric fields.
• To relate protein DEP responses to molecular-level dielectric properties and hydration effects.

Main Methods:

• Developed a novel DEP force equation incorporating dielectric increments (δε+, δε-) and a cross-correlated dipole interaction parameter (Γpw).
• Analyzed the limitations of macroscopic dielectric mixture theories for solvated proteins.
• Evaluated the equation using experimental data for 12 different proteins.

Main Results:

• The new equation successfully relates DEP response to protein dielectric properties and effective volume.
• A consistent value for the hydration interaction parameter Γpw (≈4600 ± 120) was found for 9 out of 12 proteins.
• Observed protein polarizability exceeding intrinsic values suggests potential relaxor ferroelectric nanodomains in hydration shells.

Conclusions:

• The proposed DEP force equation provides a more accurate framework for understanding protein dielectrophoresis.
• Protein hydration shells play a crucial role in their dielectric response and DEP behavior.
• The findings challenge existing dielectric mixture theories and suggest novel nanoscale phenomena in protein hydration.