Method and apparatus for making quantitative measurements of localized accumulations of magnetic particles

• US 6,275,031 B1
• Filed: 05/22/2000
• Issued: 08/14/2001
• Est. Priority Date: 11/21/1997
• Status: Expired due to Term

• Current Assignee: Quantum Design International, Inc.
• Original Assignee: Quantum Design, Inc.
• Inventors: Simmonds, Michael Bancroft
• Primary Examiner(s): PATIDAR, JAY M
• Application Number:
  US09/576,103
• Time in Patent Office: 449 Days
• Field of Search: 324/201, 324/237, 324/225, 324/204, 324/226, 324/71.1, 324/71.4, 324/232, 324/233, 324/234, 324/236, 324/243, 324/239, 422/68.1, 436/526
• US Class Current: 324/239
• CPC Class Codes: B82Y 15/00 Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• CPC Class Codes: G01N 27/745 for detecting magnetic beads used in biochemical assays concerning the assays G01N33/54326; sensors therefor G01R33/1269; automatic analysers therefor G01N35/0098
• CPC Class Codes: G01N 35/0098 involving analyte bound to insoluble magnetic carrier, e.g. using magnetic separation magnetic particles used in immunoassays G01N33/54326; magnetic separation in general B03C

Abstract

Apparatus for quantitatively measuring groups of magnetic particles. The particles are complexed with substances to be determined and are excited in a magnetic field. The magnetic particles are thereby caused to oscillate at the excitation frequency in the manner of a dipole to create their own fields. These fields are inductively coupled to sensing coils fabricated in a gradiometer configuration. The output signals from the sensing coils are appropriately amplified and processed to provide useful output indications.

Claims

1. Apparatus for making quantitative measurements of target analyte formed in complex samples comprised of magnetic particles of known size and magnetic characteristics bound to the target analyte, said apparatus comprising:

a movable substrate in which the samples are deposited in defined patterns;

magnetic field sensing elements having output signal conductors;

apparatus for moving said samples into the magnetic field and into operative relationship with said sensing elements which have resultant output signals; and

a signal processor for converting said output signals from said sensing elements to provide a signal indicative of the quantity of said samples in a pattern.

2. The apparatus of claim 1, wherein said sensing elements are inductive sensing coils.

3. The apparatus of claim 2, wherein said sensing elements are two spaced said sensing coils.

4. The apparatus of claim 3, wherein said sensing coils are connected in a gradiometer configuration.

5. The apparatus of claim 3, wherein said sensing coils are circular spirals.

6. The apparatus of claim 3, wherein said sensing coils are rectangular in shape.

7. The apparatus of claim 1, wherein said moving apparatus provides two dimensional relative motion between said samples and said magnetic field applying means.

8. The apparatus of claim 7, wherein said moving apparatus comprises:

a motor and screw arrangement for moving the magnetic field generating means linearly with respect to said movable substrate; and

a motor arrangement for moving said movable substrate and samples past the magnetic field generating means in a predetermined manner.

9. The apparatus of claim 8, wherein:

said movable substrate is a disc shaped and configured to receive a plurality of patterns of samples; and

said motor is a stepper motor adapted to rotate said disc in accordance with signals from said signal processor.

10. The apparatus of claim 1, wherein said magnetic field generating means comprises:

a toroid core having a gap in one side;

a drive coil wound around said core and leaving said gap clear; and

means for applying AC power to said drive coil.

11. The apparatus of claim 10, and further comprising a feedback loop coupled to said core and drive coil, the output of said feedback loop being connected to said signal processor to enable said signal processor to self correct for external influences.

12. The apparatus of claim 10, wherein said sensing elements are mounted on a sensor substrate in fixed relationship with and extending, into said gap.

13. The apparatus of claim 12, wherein said sensing, elements are two spaced sensing coils mounted on said sensor substrate and connected in a gradiometer configuration, said sensing coils being positioned in said gap.

14. The apparatus of claim 13, wherein said sensor substrate is elongated and has on its proximal end bonding pads to which are connected conductors for input to and output signals from said sensing coils which are mounted on the distal end of said sensor substrate, said sensor substrate further comprising a conductive shield around said bonding pads and said proximal end of said sensor substrate to reduce stray signal and interference pickup.

15. The apparatus of claim 1, wherein said signal processor comprises:

an amplifier coupled to the output of said sensing elements;

a phase sensitive detector connected to said amplifier to condition the output signals;

an analog to digital converter to convert the output signals to digital form; and

computation means for receiving said digitized signals and converting them to human useful form and to provide control signals to said apparatus.

16. A method for quantitatively measuring target analyte coupled to magnetic particles to form magnetic bound complex samples, said particles having magnetic moments and magnetic fields associated with said moments, said method comprising:

applying at least one sample pattern in a predetermined configuration on a substrate;

creating a time varying magnetic field in a predefined location;

moving the sample pattern through the magnetic field in a predefined manner to excite the magnetic particles in the pattern and cause a change in the magnetic moments therein;

sensing the fields associated with the magnetic moments of the particles; and

creating a signal representative of the quantity of magnetic particles present.

17. The method recited in claim 16, wherein said sensing step is accomplished by a pair of sensing coils connected in a gradiometer configuration.

18. The method recited in claim 16, wherein the substrate is rotatable disc.

19. The method recited in claim 16, wherein the magnetic field is created in a gap in a toroidal core having a drive coil wound therearound.

20. The method recited in claim 19, and comprising the further steps of:

applying groups of sample patterns spaced around at least a portion of the periphery of the disc;

moving the disc periphery into the gap in the toroidal core; and

rotating the disc so that the sample patterns pass through the gap.

21. The method recited in claim 16, wherein the magnetic field is created on a toroidal core having a drive coil wound therearound and the creating step is accomplished by means of a signal processor, said method comprising the further steps of:

applying an AC drive signal to a drive coil to create the magnetic field;

feeding back a signal representative of the AC drive signal in the drive coil to the signal processor; and

correcting errors in the signal processor resulting from external influences by using the feedback signal.

22. Apparatus for making quantitative measurements of target analyte, said apparatus comprising:

a movable substrate configured to receive samples including said target analyte in defined patterns thereon, said samples being comprised of magnetic particles of known size and magnetic characteristics bound to the target analyte to form magnetic bound complex samples;

a magnetizer for generating a time varying magnetic field;

magnetic field sensing elements having output signal conductors;

apparatus for moving said samples into the magnetic field and into operative relationship with said sensing elements which have resultant output signals; and

a signal processor for converting said output signals from said sensing elements to provide a signal indicative of the quantity of said analyte in a pattern.

23. A method for quantitatively measuring target analyte, said method comprising:

applying at least one sample pattern in a predetermined configuration on a substrate, the sample pattern being comprised of magnetic particles of known size and magnetic characteristics coupled to the target analyte to form magnetic bound complex samples, said particles having magnetic moments and magnetic fields associated with said moments;

applying a time varying magnetic field in a predefined location;

moving the sample pattern through the applied magnetic field in a predefined manner to excite the magnetic particles in the pattern and cause a change in the magnetic moments therein;

sensing the fields associated with the magnetic moments of the particles; and

creating a signal representative of the quantity of magnetic particles present.