Surface conductance and other properties of latex particles measured by electrorotation

Biochimica et Biophysica Acta (BBA) - General Subjects

Green

et al. 2003

The dielectric properties of the Tobacco Mosaic Virus (TMV) have been measured using time domain dielectric spectroscopy (TDDS) in the temperature range from 1 to 40 jC. A single dielectric dispersion is observed in the MHz range. The activation energy of the process is found to be in the range 1 -2 kcal/mol. The experimental data could not be completely accounted for by current theoretical models, but evidence indicates that the dielectric loss arises from polarisation of charge on and around the virus. D

Section: Interfacial Polarisationmentioning

confidence: 99%

Dielectric spectroscopy of Tobacco Mosaic Virus

Ermolina

Biochimica et Biophysica Acta (BBA) - General Subjects

Green

et al. 2003

“…Recent data concerning the dielectrophoretic properties of latex particles shows that the polarisation of the particles is dominated by surface conductance [26][27][28]. O'Konski's theory of constant surface conductance can explain the AC electrokinetic behaviour of micrometre-sized latex particles [28].…”

Section: Introductionmentioning

confidence: 99%

“…O'Konski's theory of constant surface conductance can explain the AC electrokinetic behaviour of micrometre-sized latex particles [28]. However, it does not adequately model the behaviour of submicrometre latex particles [26,27].…”

Section: Introductionmentioning

confidence: 99%

The electrokinetic properties of latex particles: comparison of electrophoresis and dielectrophoresis

Ermolina

Journal of Colloid and Interface Science

2005

223

255

A comprehensive study of the AC and DC electrokinetic properties of submicrometre latex particles as a function of particle size and suspending medium conductivity and viscosity is presented. Electrophoretic mobility and dielectrophoretic cross-over results were measured for particle diameters ranging from 44 to 2000 nm. The zeta potentials of the particles were calculated from the electrophoretic mobility data for different suspending medium conductivities, using various models, with and without the inclusion of surface conduction. The dielectrophoretic data was analysed to derive values for the Stern layer conductance and zeta potentials.  2004 Elsevier Inc. All rights reserved.

“…The dielectrophoretic force is governed by the real part of this expression and for latex particles is dominated by conductivity effects. The conductivity of a colloidal particle consists of two components [14,15] a bulk and surface component given by σ p = σ s + 2Ks a , where σ s is the bulk conductivity of the particle of radius a, which can be assumed to be approximately zero for latex spheres. The surface conductance, K s , arises from the movement of ions in the electrical double layer and is directly proportional to the surface charge density.…”

mentioning

confidence: 99%

Dielectrophoretic separation of nano-particles

Green

J. Phys. D: Appl. Phys.

1997

156

141

Abstract. We show for the first time that it is possible to separate a population of nanoparticles into two subpopulations solely on the basis of their dielectric properties. Using nanofabricated electrode arrays it has been shown that a solution of 93 nm diameter latex beads with a distribution of surface charge can be separated by the application of non-uniform AC electric fields (dielectrophoresis). The mixture separated into two populations, one experiencing positive dielectrophoresis and the other negative dielectrophoresis.The movement of polarizable particles in non-uniform fields, termed dielectrophoresis by Pohl [1], has been exploited as a rapid non-invasive tool for the diagnosis and separation of mammalian cells and micro-organisms [2]. It has found practical applications in medicine for separating cancer cells from blood [3], enriching CD34+ cells in bone marrow samples [4] and for detecting the viability of pathogenic organisms in water [5].Separation of particles is based on the fact that when placed in a non-uniform AC electric field, polarized particles experience a variable translational force, depending on the applied field frequency. For particles whose polarizability is greater than the medium the net movement is to regions of highest field strength, whereas particles whose polarizability is less than the medium move to the region of lowest field gradient. Because the particle's polarization is frequency dependent, the net force is also frequency dependent. Therefore, by judicious choice of suspending medium conductivity and applied frequency, even particles with very similar dielectric properties can be efficiently separated.The sum total of the forces on a given particle is: F total = F deterministic + F random . The deterministic force is the sum of the sedimentation, hydrodynamic and dielectrophoretic forces. The random force is due to Brownian motion and for particles with a diameter of the order of 100 nm this force is considerable. The mean free path of the movement is inversely dependent on mass, implying that decreases in the particle diameter require significant increases in the applied electrostatic energy (or field strength). The stable trapping of viruses and beads has been demonstrated previously [6][7][8][9]. Here we show that nanometre sized latex spheres can be both stably trapped in nanofabricated electrode arrays and, more importantly, that a heterogeneous mixture can be separated into two populations using dielectrophoresis. Experiments were conducted on charged latex spheres of 93 nm diameter, using planar electrodes manufactured by electron-beam lithography. The applied electric field strength was 2.5 × 10 5 V m −1 and the suspending medium conductivity was 0.018 S m −1 . Large electric field strengths cause localized heating of electrode structures which in turn gives rise to discontinuities in conductivity, permittivity and viscosity of the medium. The result is the inception