Active microrheology of protein condensates using colloidal probe-AFM

Area of Science:

• Biophysics
• Materials Science
• Soft Matter Physics

Background:

• Protein condensates, formed by liquid-liquid phase separation, are studied for bio-adhesion, coatings, and as models for cellular membraneless organelles.
• Understanding the interfacial mechanics and rheology of these micro-scale condensates is critical for both biological insights and technological advancements.

Purpose of the Study:

• To demonstrate a novel method for simultaneously investigating interfacial mechanics and dynamic rheological properties of micro-scale protein condensates.
• To characterize the frequency-dependent mechanical behavior of protein condensates across a broad range of time scales.

Main Methods:

• Utilized colloidal probe atomic force microscopy (AFM) with an oscillating tip to probe micro-scale protein condensates.
• Formed protein condensates via controlled capillary condensation.
• Analyzed data using an equivalent mechanical model across oscillation frequencies from 1 to 10⁴ rad/s.

Main Results:

• Identified three characteristic frequency domains governing the mechanics of micro-scale protein condensates.
• Observed an interfacial tension-dominated domain at low frequencies.
• Found a transition domain (viscous-to-elastic crossover) at intermediate frequencies and an elasticity-dominated domain at high frequencies.

Conclusions:

• The developed AFM approach provides a comprehensive method to study the complex rheology of protein condensates.
• The identified frequency domains offer a framework for understanding protein condensate behavior in biological systems and for designing advanced materials.