CiteULike: weeks's particle-tracking

Confocal microscopy of colloidal particles: Towards reliable, optimum coordinates

MC Jenkins — 2008-02-19T17:20:12-00:00

Advances in Colloid and Interface Science, Vol. 136, No. 1-2. (15 January 2008), pp. 65-92.

Over the last decade, the light microscope has become increasingly useful as a quantitative tool for studying colloidal systems. The ability to obtain particle coordinates in bulk samples from micrographs is particularly appealing. In this paper we review and extend methods for optimal image formation of colloidal samples, which is vital for particle coordinates of the highest accuracy, and for extracting the most reliable coordinates from these images. We discuss in depth the accuracy of the coordinates, which is sensitive to the details of the colloidal system and the imaging system. Moreover, this accuracy can vary between particles, particularly in dense systems. We introduce a previously unreported error estimate and use it to develop an iterative method for finding particle coordinates. This individual-particle accuracy assessment also allows comparison between particle locations obtained from different experiments. Though aimed primarily at confocal microscopy studies of colloidal systems, the methods outlined here should transfer readily to many other feature extraction problems, especially where features may overlap one another.

Single-Particle Colloid Tracking in Four Dimensions

SM Anthony — 2006-12-07T16:14:51-00:00

Langmuir, Vol. 22, No. 24. (21 November 2006), pp. 9812-9815.

Coating a close-packed fluorescent colloid monolayer with a nanometer-thick metal film followed by sonication in liquid produces modulated optical nanoprobes. The metal coating modulates the fluorescence as these structures rotate in suspension, enabling the use of these particles as probes to monitor both rotational and center-of-mass (translational) dynamics in complex environments. Here, we demonstrate methods to simultaneously measure two translational and two rotational degrees of freedom, with excellent agreement to theory. The capability to determine two angles of rotation opens several new avenues of future research.

Particle Tracking Microrheology of Complex Fluids

TG Mason — 2006-08-30T16:25:45-00:00

Physical Review Letters, Vol. 79, No. 17. (27 October 1997), 3282.

We present a new method for measuring the linear viscoelastic shear moduli of complex fluids. Using photodiode detection of laser light scattered from a thermally excited colloidal probe sphere; we track its trajectory and extract the moduli using a frequency-dependent Stokes-Einstein equation. Spectra obtained for polyethylene oxide in water are in excellent agreement with those found mechanically and using diffusing wave spectroscopy. Since only minute sample volumes are required; this method is well suited for biomaterials of high purity; as we demonstrate with a concentrated DNA solution.

Self-Diffusion in Concentrated Colloid Suspensions Studied by Digital Video Microscopy of Core-Shell Tracer Particles

A Kasper — 2007-05-18T06:56:19-00:00

Langmuir, Vol. 14, No. 18. (1 September 1998), pp. 5004-5010.

Abstract: Optical video microscopy and digital image processing have been used to study the self-diffusion of colloidal particles with a hard-sphere potential. The colloid particles consist of cross-linked polymers and are dispersed in a good solvent to avoid aggregation. To investigate single particle motion in highly concentrated dispersions, a host-tracer system, consisting of two different kinds of polymer particles, has been designed: the host particles are made of poly-t-butylacrylate (with ethanedioldiacrylate as cross-linker) and have the same refractive index as the employed solvent, 4-fluorotoluene. The tracer particles have a core-shell structure with a polystyrene core (cross-linked with m-diisopropenylbenzene) and a shell consisting of cross-linked poly-t-butylacrylate to match surface properties and interaction potential to those of the "invisible" particles. The motion of the strongly scattering core-shell particles ("tracer" particles) was observed by dark-field light microscopy. From the obtained particle trajectories, mean squared displacements, van Hove autocorrelation functions, and vector-vector correlation functions were calculated, yielding a direct real-space image of the "cage effect" at = 0.52 and of the transition to a glassy state between = 0.56 and = 0.60, as expected for a hard sphere system. The extracted long-time self-diffusion coefficients Dself,long are fully consistent with a recent theoretical prediction using full many-body hydrodynamics at 0.56 and a colloid glass transition at g = 0.583. However, even at = 0.60, Dself,long seems to be still finite, possibly indicating the existence of long-time motion of colloidal particles even in the glassy state.

Particle Tracking Using IDL: website

Eric Weeks — 2007-09-24T16:32:57-00:00

Video microscopy of colloidal suspensions and colloidal crystals

Piotr Habdas — 2007-09-20T04:33:58-00:00

Current Opinion in Colloid & Interface Science, Vol. 7, No. 3-4. (August 2002), pp. 196-203.

Colloidal suspensions are simple model systems for the study of phase transitions. Video microscopy is capable of directly imaging the structure and dynamics of colloidal suspensions in different phases. Recent results related to crystallization, glasses, and 2D systems complement and extend previous theoretical and experimental studies. Moreover, new techniques allow the details of interactions between individual colloidal particles to be carefully measured. Understanding these details will be crucial for designing novel colloidal phases and new materials, and for manipulating colloidal suspensions for industrial uses.

Methods of Digital Video Microscopy for Colloidal Studies

John Crocker — 2007-05-18T07:19:49-00:00

Journal of Colloid and Interface Science, Vol. 179, No. 1. (15 April 1996), pp. 298-310.

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 submicrometer 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.