# US 9,518,957 B2 · Magnetic signal measuring apparatus and magnetic signal measuring method

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- Number: US 9,518,957 B2
- Document ID: US9518957B2
- Status: Granted
- Kind: B2
- Application number: 14/607,187
- Filed: 2015-01-28
- Published: 2015-09-03
- Granted: 2016-12-13
- Earliest claimed: 2014-02-28
- Assignees: Hitachi, Ltd.
- Applicants: Hitachi, Ltd.
- Inventors: Keiji Enpuku; Takako Mizoguchi; Akihiko Kandori
- Web page: https://patentgrep.com/patent/US9518957B2

## CPC

- G01N 27/72: by investigating magnetic variables
- 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)}
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

A magnetic signal measuring apparatus includes a first magnetic field applying unit that applies a first magnetic field to magnetic substances when a measured substance is binding to the magnetic substances, a second magnetic field applying unit that applies a second magnetic field to the magnetic substances to which the first magnetic field has been applied, and a SQUID that measures a magnetic signal derived from the magnetic substances. The first magnetic field has an intensity of such a degree that the magnetic substances do not flocculate with each other and such a degree that directions of magnetic moments in the magnetic substances can be aligned with each other. The second magnetic field has an intensity of such a degree that the magnetic substances do not flocculate with each other and such a degree that a magnetic signal can be obtained from the magnetic substances.

## Claims

### Claim 1

A magnetic signal measuring apparatus comprising:
a first magnetic field applying unit that is arranged to apply a first magnetic field to a sample in which a plurality of magnetic substances and a measured substance able to bind to the magnetic substances are mixed together in an unbound state, the first magnetic field having an intensity of such a degree that the magnetic substances do not flocculate with each other and such a degree that directions of magnetic moments in the magnetic substances can be aligned with each other;
a second magnetic field applying unit that is arranged to apply a second magnetic field to the magnetic substances to which the first magnetic field has been applied, the second magnetic field having an intensity of such a degree that the magnetic substances do not flocculate with each other and such a degree that a magnetic signal can be obtained from the magnetic substances; and
a measurement unit that is arranged to measure the magnetic signal derived from the magnetic substances.

### Claim 2 (depends on 1)

The magnetic signal measuring apparatus according to claim 1, wherein the intensity Hr of the first magnetic field has a lower limit which is defined by the following expression (1):
(mHr)/(kBT)>1 (1)
where m indicates a magnitude of a magnetic moment of the magnetic substance; Hr indicates the intensity of the magnetic field; kB=1.38×10−23 indicates the Boltzmann constant; and T indicates a temperature.

### Claim 3 (depends on 1)

The magnetic signal measuring apparatus according to claim 1, wherein the intensity of the second magnetic field has an upper limit which meets a value of Um/Pn defined by the following expression (2):
Um/Pn<1 (2)
where Um is defined by the following expression (3) and Pn is defined by the following expression (4):
Um=−μ0m2/2πd3 (3)
Pn=kBT (4)
where μ0 indicates a vacuum magnetic permeability; m indicates a magnitude of a magnetic moment of the magnetic substance; d indicates a distance between the magnetic substances; kB=1.38×10−23 indicates the Boltzmann constant; and T indicates a temperature.

### Claim 4 (depends on 1)

The magnetic signal measuring apparatus according to claim 1, wherein the sample is a liquid sample in which the magnetic substances and the measured substance exist in a solution.

### Claim 5

A magnetic signal measuring method implemented by a magnetic signal measuring apparatus that measures a magnetic signal derived from a plurality of magnetic substances binding to a measured substance, the magnetic signal measuring method comprising:
applying a first magnetic field to a sample in which the magnetic substances and the measured substance are mixed together in an unbound state, the first magnetic field having an intensity of such a degree that the magnetic substances do not flocculate with each other and such a degree that directions of magnetic moments in the magnetic substances can be aligned with each other;
applying a second magnetic field to the magnetic substances to which the first magnetic field has been applied, the second magnetic field having an intensity of such a degree that the magnetic substances do not flocculate with each other and such a degree that the magnetic signal can be obtained from the magnetic substances; and
measuring the magnetic signal derived from the magnetic substances.

### Claim 6 (depends on 5)

The magnetic signal measuring method according to claim 5, wherein the intensity Hr of the first magnetic field has a lower limit which is defined by the following expression (1):
(mHr)/(kBT)>1 (1)
where m indicates a magnitude of a magnetic moment of the magnetic substance; Hr indicates the intensity of the magnetic field; kB=1.38×10−23 indicates the Boltzmann constant; and T indicates a temperature.

### Claim 7 (depends on 5)

The magnetic signal measuring method according to claim 5, wherein the intensity of the second magnetic field has an upper limit which meets a value of Um/Pn defined by the following expression (2):
Um/Pn<1 (2)
where Um is defined by the following expression (3) and Pn is defined by the following expression (4):
Um=−μ0m2/2πd3 (3)
Pn=kBT (4)
where μ0 indicates a vacuum magnetic permeability; m indicates a magnitude of a magnetic moment of the magnetic substance; d indicates a distance between the magnetic substances; kB=1.38×10−23 indicates the Boltzmann constant; and T indicates a temperature.

### Claim 8 (depends on 5)

The magnetic signal measuring method according to claim 5, wherein the sample is a liquid sample in which the magnetic substances and the measured substance exist in a solution.