Modeling Active Particle Motion from Fluorescence Correlation Spectroscopy Data

Area of Science:

• Colloid and Interface Science
• Soft Matter Physics
• Nanotechnology

Background:

• Active colloids are engineered micro/nanomotors with diverse propulsion mechanisms.
• Comparing 2D and 3D analysis techniques for active colloids is crucial but challenging.
• Fluorescence correlation spectroscopy (FCS) offers a 3D volumetric approach.

Purpose of the Study:

• To compare 3D FCS measurements with 2D optical tracking for active colloids.
• To establish FCS detectability criteria for active colloids.
• To quantify locomotion and distinguish between active and passive colloids.

Main Methods:

• Utilized fluorescence correlation spectroscopy (FCS) for 3D particle motion analysis.
• Employed standard 2D optical microscopy-based tracking.
• Investigated three propulsion types: self-diffusiophoresis, bubble propulsion, and magnetic guidance.

Main Results:

• FCS successfully quantified locomotion in single and mixed active/passive colloid populations.
• Directed particle motion assessed by FCS yielded velocities comparable to optical tracking.
• Consistent trends in motor dynamics were observed, though absolute diffusion coefficients differed.

Conclusions:

• FCS is a reliable method for assessing active colloid transport properties with appropriate data treatment.
• FCS and optical tracking are complementary, providing population-level and individual motor diffusivity, respectively.
• This study bridges the gap between 2D and 3D analysis methods for active matter.