Challenges in determining anomalous diffusion in crowded fluids.

Area of Science:

• Biophysics
• Physical Chemistry
• Cell Biology

Background:

• Anomalous diffusion is frequently observed in crowded biological environments like the cell cytoplasm.
• The microscopic origins of anomalous diffusion remain poorly understood despite various experimental observations.

Purpose of the Study:

• To quantitatively compare two common techniques for assessing anomalous diffusion: single particle tracking (SPT) and fluorescence correlation spectroscopy (FCS).
• To investigate the impact of experimental factors, such as positional uncertainty in SPT, on the measurement of diffusion anomalies.

Main Methods:

• Extensive computer simulations of two distinct random walk models: fractional Brownian motion and obstructed diffusion.
• Quantitative comparison of diffusion anomaly results obtained from simulated SPT and FCS data.

Main Results:

• Simulated SPT and FCS yield equivalent results for diffusion anomalies in both fractional Brownian motion and obstructed diffusion models.
• Positional uncertainties inherent in SPT experiments systematically underestimate the diffusion anomaly.
• This underestimation effect is significant when positional uncertainty exceeds the average displacement between frames.

Conclusions:

• SPT and FCS are comparable techniques for characterizing anomalous diffusion in simulations.
• Positional uncertainty is a critical factor to consider in SPT experiments, potentially leading to underestimation of diffusion anomalies.
• Further research is needed to refine SPT methodologies to account for positional uncertainties in biological systems.