Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Patent
1995-01-27
1996-10-29
Gorgos, Kathryn
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
204643, 204600, 204450, G01N 2726
Patent
active
055693679
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method and apparatus for the separation of particles, including micro-organisms, utilising the phenomenon of dielectrophoresis.
It is well known that dielectrically polarisable particles in a non-uniform electrical field are subject, even If they have no net charge, to a "dielectrophoretic" force if the effective polarizability of the particles is different to that of the surrounding medium. The movement is determined by the dielectric properties (conductivity and permittivity) rather than by the charge of the particles, as in the wider known phenomenon of electrophoresis. The force F to which a particle of volume v and effective polarizability p is subject is given by the relation .gradient. is the del vector operator.
In an alternating field in which the field strength at any point is oscillatory but the field pattern remains stationary, the dielectrophoretic force on a particle is oscillatory but unidirectional, even though the electric field varies cyclically. The particles, if they are polarisable more than the medium in which they are suspended move In the direction of increasing electric field strength which means, usually towards one of a plurality of electrodes between which the field is established. The polarizability of a particle, and therefore the polarity and magnitude of the dielectrophoretic force upon it, will vary as a function of the frequency of the applied field because the dielectric properties of all materials have characteristic frequency dependent components.
Separators such as column separators employ a matrix to retain the particles temporarily as they flow through the column; the retention time is dependent upon a physical property of the particle. As a mixture of particles passes through the matrix different types of particles are retarded at different rates and separate into fractions. In chromatographic separators the retardation of the particles is caused by their size and in ion exchange separators the retardation of particles is dependent upon their ionic strength. Electrophoretic separators rely on the charge carried by the particles and neutral particles must first be given a charge before the separation can occur. The charged particles are then passed through a matrix under the influence of an electric field, which retards the different types of particles according to their size and charge. In all of these separators the order in which the fractions are passed out is constrained and depends upon the type of separator and the type of matrix.
The known devices for dielectrophoretic spectra analysis are designed to retain the particles between the electrodes for the examination of some property of the collected particles in order to determine the type or quantity of particles present. However, a long retention time increases the probability of the particles (especially cells) sticking permanently to the electrodes.
Separation of charged particles by electrophoresis as described by U.S. Pat. No. 4,061,560, requires the use of a buffer solution and the zeta potential of the system is influenced by the introduction of electrolytes to the buffer solution.
U.S. Pat. No. 4,441,972 discloses techniques for the breakdown of cells and subsequent fusing of the contents of contiguous cells. It also teaches separating or sorting of cells for examination only, the cells being thereafter collected and withdrawn.
According to one aspect of the invention there is provided apparatus for separating a mixture of particles comprising a chamber with an inlet and an outlet, means for providing an eluant flow between said inlet and said outlet, within the chamber an electrode structure of at least two electrodes, means for applying an alternating voltage between the electrodes, said electrode structure being such that when energized in operation of the apparatus there Is established in the eluant a spatially non-uniform alternating field, whereby particles caused to flow through the chamber In said eluant flow are carried past the electrode structure and are separated
REFERENCES:
patent: 3795605 (1974-03-01), Candor
patent: 3893898 (1975-07-01), Candor
patent: 4061560 (1977-12-01), Hannig et al.
patent: 4326934 (1982-04-01), Pohl
patent: 4441972 (1984-04-01), Pohl
Betts Walter B.
Hawkes Jeremy J.
British Technology Group Limited
Gorgos Kathryn
Noguerola Alex
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