Liquid purification or separation – Processes – Using magnetic force
Reexamination Certificate
2000-01-03
2001-05-08
Savage, Matthew O. (Department: 1723)
Liquid purification or separation
Processes
Using magnetic force
C436S526000
Reexamination Certificate
active
06228268
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for mixing and separation of magnetic Particles for the purpose of isolating substances of interest from a nonmagnetic liquid test medium.
2. Description of Related Art
Magnetic separation of biomolecules and cells based on magnetic particles and employing biospecific affinity reactions is advantageous in terms of selectivity, simplicity, and speed. The technique has proved to be quite useful in analytical and preparative biotechnology and is now being increasingly used for bioassays and isolation of target substances such as cells, proteins, nucleic acid sequences and the like.
As used herein, the term “receptor” refers to any substance or group of substances having biospecific binding affinity for a given liquid, to the substantial exclusion of other substances. Among the receptors susceptible to biospecific binding affinity reactions are antibodies (both monoclonal and polyclonol), antibody fragments, enzymes, nucleic acids, lectins and the like. The term “ligand” refers to substances such as antigens, haptens, and various cell associated structures having at least one characteristic determinant or epitope, which substances are capable of being biospecifically recognized by and bound to a receptor. The term “target substance” refers to either member of a biospecific binding affinity pair, i.e., a pair of substances or a substance and a structure exhibiting a mutual affinity of interaction, and includes such things as biological cells or cell components, biospecific ligands, and receptors.
Affinity separation refers to known process techniques where a target substance mixed with other substances in a liquid medium is bound to the surface of a solid phase by a biospecific affinity binding reaction. Substances, which lack the specific molecule or structure of the target substance, are not bound to the solid phase and can be removed to effect the separation of the bound substance or vice versa. Small particles, particularly polymeric spherical particles as solid phase, have proved to be quite useful, as they can be conveniently coated with biomolecules, provide a very high surface area, and give reasonable reaction kinetics. Separations of the particles containing bound target substance (bound material) from the liquid medium (free material) may be accomplished by filtration or gravitational effects, e.g., settling, or by centrifugation.
Separation of bound/free fractions is greatly simplified by employing magnetizable particles which allows the particle bound substance to be separated by applying a magnetic field. Small magnetizable particles are well known in the art as their use in the separations involving immunological and other biospecific affinity reactions. Small magnetizable particles generally fall into two broad categories. The first category includes particles that are permanently magnetized, and the second comprises particles that become magnetic only when subjected to a magnetic field. The latter are referred to as paramagnetic or superparamagnetic particles and are usually preferred over the permanently magnetized particles.
For many applications, the surface of paramagnetic particles is coated with a suitable ligand or receptor, such as antibodies, lectins, oligonucleotides, or other bioreactive molecules, which can selectively bind a target substance in a mixture with other substances. Examples of small magnetic particles or beads are disclosed in U.S. Pat. No. 4,230,685; U.S. Pat. No. 4,554,088; and U.S. Pat. No. 4,628,037. The use of paramagnetic particles is taught in publications, “Application of Magnetic Beads in Bioassays,” by B. Haukanes and C. Kvam, Bio/Technology, 11:60-63 (1993); “Removal of Neuroblastoma Cells from Bone Marrow with Monoclonal Antibodies Conjugated to Magnetic Microspheres” by J. G. Treleaven et. al., Lancet, Jan. 14, 1984, pages 70-73; “Depletion of T Lymphocytes from Human Bone Marrow,” by F. Vartdal et. al., Transplantation, 43: 366-71 (1987); “Magnetic Monosized Polymer Particles for Fast and Specific Fractionation of Human Mononuclear Cells,” by T. Lea et. al., Scandinavian Journal of Immunology, 22: 207-16 (1985); and “Advances in Biomagnetic Separations,” (1994), M. Uhlen et. al. eds. Eaton Publishing Co., Natick, Mass.
The magnetic separation process typically involves mixing the sample with paramagnetic particles in a liquid medium to bind the target substance by affinity reaction, and then separating the bound particle/target complex from the sample medium by applying a magnetic field. All magnetic particles except those particles that are colloidal, settle in time. The liquid medium, therefore, must be agitated to some degree to keep the particles suspended for a sufficient period of time to allow the bioaffmity binding reaction to occur. Examples of known agitation methods include shaking, swirling, rocking, rotation, or similar manipulations of a partially filled container. In some cases the affinity bond between the target substance and the paramagnetic particles is relatively weak so as to be disrupted by strong turbulence in the liquid medium. In other cases biological target substances such as cells, cellular fractions, and enzyme complexes are extremely fragile and will likewise be disrupted or denatured by excess turbulence.
Excess turbulence is just one of several significant drawbacks and deficiencies of apparatus and methods used in the prior art for biomagnetic separations. The specified configuration of a magnetic separation apparatus used for separating particle-bound target complex from the liquid medium will depend on the nature and size of magnetic particles. Paramagnetic particles in the size range of 0.1 to 300 (m are readily removed by means of commercially-available magnetic separation devices. Examples of such magnetic separation devices are the Dynal MPC series of separators manufactured by Dynal, Inc., Lake Success, N.Y.; and BioMag Separator series devices manufactured by PerSeptive Diagnostics, Cambridge, Mass.; and a magnetic separator rack described in U.S. Pat. No. 4, 895,650. These devices employ permanent magnets located externally to a container holding a test medium and provide only for separation. Mixing of the paramagnetic particles in the test medium for affinity binding reaction must be done separately. For example, Dynal MPC series of separators requires a separate mixing apparatus, a Dynal Sample Mixer, for agitating the test media. The process must be actively monitored through various stages of mixing, washing, and separation, and requires significant intervention from the operator. Accordingly, the efficiency of these devices is necessarily limited by the skill and effectiveness of the operator.
U.S. Pat. No. 4,910,148 describes a device and method for separating cancer cells from healthy cells. Immunoreactive paramagnetic particles and bone marrow cells are mixed by agitating the liquid medium on a rocking platform. Once the particles have bound to the cancer cells, they are separated from the liquid medium by magnets located externally on the platform. Although such mixing minimizes the liquid turbulence, it does not provide an efficient degree of contact between the particles and the target substance. Moreover, the utility of this device is limited to the separation of cells from relatively large sample volumes.
U.S. Pat. No. 5,238,812 describes a complicated device for rapid mixing to enhance bioaffinity binding reactions employing a U-tube-like structure as mixer. The U-tube is rapidly, rocked or rotated for 5 to 15 seconds to mix the magnetic particles in the test medium, and then a magnet is brought in close proximity to the bottom of the U-tube to separate the magnetic particles. As stated in the '812 patent, its utility is limited to treating very small volumes (<1000 (l) of test medium.
U.S. Pat. No. 5,336,760 describes a mixing and magnetic separation device comprising a chamber attached to a platform with one or more magnets located close to the conta
Patent Imaging Corporation
Savage Matthew O.
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