Introduction

Methods of Digital Video Microscopy for Colloidal Studies

John C. Crocker and David G. Grier

Abstract:

We describe a set of image processing algorithms for extracting quantitative data from digitized video microscope images of colloidal suspensions. In a typical application, these direct imaging techniques can locate submicron spheres to within 10 nm in the focal plane and 150 nm in depth. Combining information from a sequence of video images into single-particle trajectories makes possible measurements of quantities of fundamental and practical interest such as diffusion coefficients and pair-wise interaction potentials. The measurements we describe in detail combine the outstanding resolution of digital imaging with video-synchronized optical trapping to obtain highly accurate and reproducible results very rapidly.

Keywords: colloid, image processing, video microscopy, optical tweezers, dynamics, diffusion coefficient, interaction potential

• Introduction
• Typical Instrumentation
• Five Stages of Colloidal Particle Tracking
  • Image Restoration
  • Locating Particles
  • Refining Location Estimates
  • Noise Discrimination and Tracking in Depth
  • Linking Locations into Trajectories
  • Error Estimates and Optimal Settings
• Dynamical Measurements
  • Diffusion Coefficients
  • Blinking Optical Tweezers
  • Interaction Measurements
• Summary
• References
• Figures
  • Figure 1
  • Figure 2
  • Figure 3
  • Figure 4
  • Figure 5
  • Figure 6
  • Figure 7
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