Chemistry: electrical and wave energy – Apparatus – Electrophoretic or electro-osmotic apparatus
Reexamination Certificate
1998-05-15
2001-03-06
Jones, Dwayne C. (Department: 1614)
Chemistry: electrical and wave energy
Apparatus
Electrophoretic or electro-osmotic apparatus
C204S155000, C204S164000, C204S245000, C204S232000, C204S547000
Reexamination Certificate
active
06197176
ABSTRACT:
BACKGROUND OF THE INVENTION
Which invention relates to the manipulation of solid, semi-solid or liquid materials in liquid media.
A wide variety of commercial processes involve the use of liquid media having solid, semi-solid or liquid particles suspended in them. The particles may vary very widely from inert inorganic materials through to reactive materials, and organic or biological structures such as cells or parts of cells.
It has been known for some time that particles of these various types may be caused to move within a liquid medium by the use of a non-uniform electric field, and the basic phenomenon of dielectrophoresis has been extensively discussed, for example see “Dielectrophoresis”, Cambridge University Press, 1978 By H. A. Pohl and Chapter 6 of “Dielectric and Electronic Properties of Biological Materials”, John Wiley & Sons 1979 by Ronald Pethig.
Recently the application of dielectrophoresis has been suggested in the area of materials classification: the construction of a so-called “optical dielectrophoresis spectrometer” is described in Burt, Al-Ameen & Pethig, “An optical dielectrophoresis spectrometer for low-frequency measurements on colloidal suspensions”, Journal of Physics, Section E, Scientific Instrumentation, Volume 22 (1989) pages 952 to 957.
That paper, and the related paper “Applications of a New Optical Technique for Measuring the Dielectrophoretic Behaviour of Microorganisms”, Price, Burt and Pethig Biochimica et Biophysica Acta 964 (1988) pages 221 to 230, disclose the use of interdigitated electrodes deposited on a dielectric substrate to cause movement of suspended particulates by the dielectrophoretic effect.
Most previous work has been directed to the characterization of a materials by taking appropriate measurements of their electric field-induced properties. Another major application is in the use of positive dielectrophoretic forces to align biological cells between electrodes prior to their electrofusion, as described by W. M. Arnold and U. Zimmermann (“Electric Field Induced Fusion and Rotation of Cells”, Biological Membranes 5, 389-454, 1984). Also, a method and apparatus for dielectrophoretic manipulation of chemical species has been described by J. S. Batchelder (U.S. Pat. No. 4,390,403, Jun. 28, 1983). This method employs DC non-uniform electrical fields to manipulate one or more chemicals within a multi-electrode chamber so as to promote chemical reactions between the chemical species. The applied voltage may be periodically reversed in sign to decrease ionic shielding effects (see column 3, line 62 to column 4, line 3). The manipulation of the chemicals is controlled by positive dielectrophoretic forces resulting from differences in the dielectric constants of the chemical species.
In previous works of S. Masuda, M. Washizu and I. Kawabata “Movement of Blood Cells in Liquid by Nonuniform Travelling Field”, IEEE Transactions on Industry Applications, Volume 24 (1988) pages 217 to 222, blood cells were caused to move under the influence of a non-uniform travelling electric field. This field was generated by applying two, fixed-frequency, multiphased, voltage signals, related by having the same frequency and amplitude, to a series of parallel electrodes. Likewise, the rotating electric field described by W. M. Arnold and U. Zimmermann and employed to cause rotation of a single cell, is generated using either a single, phase-split, voltage signal or synchronized, identical, voltage pulses.
SUMMARY OF THE INVENTION
The present invention utilizes two or more electric fields that are generated using electrically independent voltages that do not share the same frequency of oscillation.
We have now found that if two or more non-uniform electric fields of differing frequencies are imposed, simultaneously or sequentially, on a suspension of particles of one or more than one type in a liquid, using appropriate electronic control, various reactions may be stimulated to occur in the particles in the liquid.
Thus, in accordance with a first broad aspect of the invention, a method of promoting reactions between particles suspended in a liquid is provided, the particles being of uniform type or of more than one type. The method comprises applying two or more independent non-uniform electrical fields of different frequencies to the liquid from an electrode array in such a fashion as to provoke or promote the desired reaction.
The term reaction as used herein is to be interpreted broadly as covering various chemical, biochemical and physical interactions, and large scale manipulations such as separation followed by recombination, optionally with a treatment being selectively applied to one component of a multicomponent system while so separated from the other component(s).
Whereas previous work (e.g. Batchelder) has employed differences in the dielectric constant of the manipulated chemical species to control the desired reactions, we have found that, in addition to varying the dielectric constant, varying the electrical conductivity of either or both the suspended particles and the suspending medium provides a further degree of control. In this connection (and throughout this specification) the term dielectric constant is used to refer to the real part of the complex permittivity.
The particles which may be used may be of animate or inanimate material and they may be colloidal or of some other nature.
With appropriate choice of the dielectric constant and electrical conductivity of either or both the suspended particle and suspending medium, both positive and negative dielectrophoretic forces may be employed as the manipulating agent. Preferably, in carrying out the method of the invention, at least one of the electrical fields is chosen to effect a negative dielectrophoretic force on some only of the particles in the liquid. By appropriate choice of electrode geometry, it is possible to achieve at appropriate regions within the electrode geometry, regions where particular species of particle segregate or particular particle agglomerations occur. In order to enable adequate quantities of suspension to be treated, the electrodes may take the form of a repeating pattern array, or. e.g. two electrodes may be comblike and inter-engaged with each extending part of the lying between two neighboring such parts of the other.
The present invention also provides apparatus for carrying out the method of the invention including a treatment cell including an electrode array, means for feeding a suspension of particles in a liquid to the treatment cell, and means for removing liquid from the cell. First means connected to electrodes in the cell are adapted to generate a first non-uniform electrical field within the cell, and second means connected to electrodes in the cell and adapted to generate a second non-uniform electrical field within the cell having a frequency which differs from that of the first non-uniform electrical field.
FIG. 8
shows an embodiment of the invention in which field generator
1
is the first means and field generator
2
is the second means. A means for simultaneously applying at least a first non-uniform electrical field, at a first frequency, and a second non-uniform electrical field, at a second frequency, comprises, for example, the first means and the second means.
Preferably, the electrode array is mounted on an external wall of the treatment cell. Such an arrangement preferably includes, as part of the liquid removing means, perforations in the external wall of the cell bearing the electrodes, the perforations being so located that, when the electrodes are appropriately electrically activated relative to the particles in the liquid medium in the cell and to the liquid medium itself, the liquid and particles drawn off through the perforations will differ from the general bulk characteristics of the suspension of particles in the liquid in the cell.
In the description of specific illustrated apparatus which follows, for simplicity of expression, reference is made to applying signals to electrodes. It should be understood that i
Burt Julian
Pethig Ronald
BTG International Limited
Delacroix-Muirheid C.
Jones Dwayne C.
Pillsbury Madison & Sutro LLP
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