Magnetic particles having two antiparallel ferromagnetic layers and attached affinity recognition molecules

• US 6,337,215 B1
• Filed: 12/01/1997
• Issued: 01/08/2002
• Est. Priority Date: 12/01/1997
• Status: Expired due to Term

• Current Assignee: GlobalFoundries, Inc.
• Original Assignee: International Business Machines Corporation
• Inventors: Wilson, Robert John
• Primary Examiner(s): Naff, David M.
• Application Number:
  US08/982,019
• Time in Patent Office: 1,499 Days
• Field of Search: 435/174, 435/176, 435/177, 435/180, 435/181, 435/7.1, 435/7.94, 435/173.1, 435/173.9, 435/261, 435/815, 436/518, 436/523, 436/524, 436/526, 436/528, 436/531, 436/533, 436/534, 530/810, 530/811, 530/812, 530/815, 530/816, 530/402, 530/403, 530/413, 252/62.51 R, 252/62.54, 427/127, 210/222, 210/695
• US Class Current: 436/526
• CPC Class Codes: B03C 1/01 by addition of magnetic adjuvants
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• CPC Class Codes: G01N 33/54333 Modification of conditions of immunological binding reaction, e.g. use of more than one type of particle, use of chemical agents to improve binding, choice of incubation time or application of magnetic field during binding reaction
• CPC Class Codes: G01N 33/5434 using magnetic particle immunoreagent carriers which constitute new materials per se
• CPC Class Codes: H01F 1/0054 Coated nanoparticles, e.g. nanoparticles coated with organic surfactant
• CPC Class Codes: H01F 1/20 in the form of particles, e.g. powder H01F1/147 takes precedence
• CPC Class Codes: H01F 1/44 of magnetic liquids, e.g. ferrofluids particles in a bonding agent H01F1/28, H01F1/36, H01F1/37
• CPC Class Codes: H01F 10/3268 the exchange coupling being asymmetric, e.g. by use of additional pinning, by using antiferromagnetic or ferromagnetic coupling interface, i.e. so-called spin-valve [SV] structure, e.g. NiFe/Cu/NiFe/FeMn
• CPC Class Codes: Y10S 435/815 by sorption
• CPC Class Codes: Y10S 530/811 Peptides or proteins is immobilized on, or in, an inorganic carrier

Abstract

Magnetic particles are prepared and used for selective separation of affinity bound partners in solution. The magnetic particles have large magnetic moments which can be made such that different strengths of magnetic moments and/or different magnetic field dependencies can be used to allow for separation of several affinity partners simultaneously. Magnetic particles having different magnetic moments and different attached acceptor molecules move at different rates in a magnetic field. The magnetic particles have a first ferromagnetic layer having a moment oriented in a first direction, a second ferromagnetic layer having a moment oriented in a second direction generally antiparallel to the first direction and a nonmagnetic spacer layer located between and in contact with the first and second ferromagnetic layers. The magnitude of the moment of the first ferromagnetic layer is substantially equal to the magnitude of the moment of the second ferromagnetic layer so that the magnetic particles have substantially zero net magnetic moment in the absence of an applied magnetic field. First and second antiferromagnetic layers may be in contact with and exchange coupled with the first and second ferromagnetic layers, respectively, for pinning the moments in the first and second directions. Affinity recognition molecules may be attached to a coating on the surface of the particles for selectively binding with a target molecule. When the recognition molecule is an antibody, the particles may be used in an immunoassay or to separate cells from a mixture by binding to cell surface antigens.

Claims

1. A composition of matter comprising:

a magnetic particle comprising a first ferromagnetic layer having a moment oriented in a first direction, a second ferromagnetic layer having a moment oriented in a second direction generally antiparallel to said first direction, and a nonmagnetic spacer layer located between and in contact with the first and second ferromagnetic layers, and wherein the magnitude of the moment of the first ferromagnetic layer is substantially equal to the magnitude of the moment of the second ferromagnetic layer so that the magnetic particle has substantially zero net magnetic moment in the absence of an applied magnetic field, and wherein the thickness of the magnetic particle is substantially the same as the total thickness of said layers making up the particle;

a coating on the surface of the magnetic particle; and

an affinity recognition molecule attached to the coating of the magnetic particle for selectively binding with a target molecule.

2. The composition of matter of claim 1 wherein the magnetic particle further comprises a first antiferromagnetic layer in contact with and exchange coupled with the first ferromagnetic layer for pinning the moment of the first ferromagnetic layer in said first direction.

3. The composition of matter of claim 2 wherein the magnetic particle further comprises a second antiferromagnetic layer in contact with and exchange coupled with the second ferromagnetic layer for pinning the moment of the second ferromagnetic layer in said second direction.

4. The composition of matter of claim 1 wherein the affinity recognition molecule is attached to the coating of the magnetic particle by covalent bonding.

5. The composition of matter of claim 1 wherein the affinity recognition molecule is selected from the group consisting of antibodies, antigens, lectins, hormones, enzymes and nucleic acids.