Static and dynamic errors in particle tracking microrheology

Biophys J. 2005 Jan;88(1):623-38. doi: 10.1529/biophysj.104.042457. Epub 2004 Nov 8.


Particle tracking techniques are often used to assess the local mechanical properties of cells and biological fluids. The extracted trajectories are exploited to compute the mean-squared displacement that characterizes the dynamics of the probe particles. Limited spatial resolution and statistical uncertainty are the limiting factors that alter the accuracy of the mean-squared displacement estimation. We precisely quantified the effect of localization errors in the determination of the mean-squared displacement by separating the sources of these errors into two separate contributions. A "static error" arises in the position measurements of immobilized particles. A "dynamic error" comes from the particle motion during the finite exposure time that is required for visualization. We calculated the propagation of these errors on the mean-squared displacement. We examined the impact of our error analysis on theoretical model fluids used in biorheology. These theoretical predictions were verified for purely viscous fluids using simulations and a multiple-particle tracking technique performed with video microscopy. We showed that the static contribution can be confidently corrected in dynamics studies by using static experiments performed at a similar noise-to-signal ratio. This groundwork allowed us to achieve higher resolution in the mean-squared displacement, and thus to increase the accuracy of microrheology studies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms
  • Biophysics / methods*
  • Diffusion
  • Elasticity
  • Microscopy, Video / methods
  • Models, Molecular
  • Models, Statistical
  • Models, Theoretical
  • Normal Distribution
  • Oscillometry
  • Photons
  • Reproducibility of Results
  • Time Factors
  • Water / chemistry


  • Water