Integrated gradiometer

A method of measuring magnetic field gradients on a small spatial scale, comprising the steps of:

• providing lithographically fabricated first and second magnetic field sensors with lateral spatial scales of up to about 10 microns and with a separation of up to about 10 microns to thereby form a gradiometer;
• introducing a source of local magnetic field to the proximity of the substrate;
• applying a magnetic field across the sensors to produce in the first sensor a first electrical signal proportional to a first magnetic field strength of the magnetic field at the first sensor and in the second sensor a second electrical signal proportional to a second magnetic field strength of the magnetic field at the second sensor;
• and
• comparing the first and second electrical signals to obtain an output representative of a magnitude of a magnetic field gradient across the sensors.

A method of detecting biological agents that are bound to magnetic particles, comprising the steps of:

• providing lithographically fabricated first and second magnetic field sensors with lateral spatial scales of up to about 10 microns and with a separation of up to about 10 microns to thereby form a gradiometer;
• functionalizing each of a plurality of microscopic magnetic particles with a first species;
• functionalizing a surface of the integrated gradiometer with a second species;
• positioning the functionalized magnetic particles near the sensors to allow a selective reaction binding the magnetic particle to the surface, thereby exposing each sensor to a magnetic field produced by the functionalized magnetic particles and generating a first electrical signal proportional to a first magnetic field strength of the magnetic field at the first sensor and a second electrical signal proportional to a second magnetic field strength of the magnetic field at the second sensor;
• and
• comparing the first and second electrical signals to identify the existence of a magnetic field gradient across the sensors indicative of the presence of a target agent.

An array of integrated gradiometers, comprising:

• an array of cells, wherein each cell comprises:
• a semiconducting substrate;
• a first sensor, fabricated on the semiconducting substrate and responsive to the presence of the magnetic field, for producing a first electrical signal proportional to a first magnetic field strength of the magnetic field;
• a second sensor, fabricated on the semiconducting substrate and responsive to the presence of the magnetic field, for producing a second electrical signal proportional to a second magnetic field strength of the magnetic field;
• said first and second sensors being spaced apart at a distance effective for measuring a magnetic field gradient having a spatial scale of up to about 10 μm;
• a comparator, for receiving and comparing said first and second electrical signals, and for producing an output representing a magnitude of the magnetic field gradient applied across said sensors;
• a first conductor for transmitting current bias to the cell;
• a second conductor for transmitting a sensed voltage from the cell to a sense amplifier;
• and
• an isolation element for electrically isolated the cell from the bias and signal wires and from other cells in the array.

An integrated gradiometer, comprising:

• a first magnetic field sensor fabricated on a semiconducting substrate as a Hall plate using a first conducting layer, fabricated with lateral dimensions of up to about 10 microns, and capable of producing a first electrical signal in proportion to the local magnetic field at the position of said first sensor;
• a second magnetic field sensor fabricated on the semiconducting substrate as a Hall plate using a second conducting layer, fabricated with lateral dimensions of up to about 10 microns, and capable of producing a second electrical signal in proportion to the local magnetic field at the position of said second sensor, and spatially separated from the first magnetic field sensor by a distance of up to about 10 microns;
• and
• a comparator, for receiving and comparing said first and second electrical signals, and for producing an output representing a magnitude of a magnetic field gradient applied across said sensors.

An integrated gradiometer, comprising:

• a first magnetic field sensor fabricated on a semiconducting substrate as a Hall plate using the bottom quantum well of a double quantum well heterostructure, fabricated with lateral dimensions of up to about 10 microns, and capable of producing a first electrical signal in proportion to the local magnetic field at the position of said first sensor;
• a second magnetic field sensor fabricated on the semiconducting substrate as a Hall plate using the top quantum well of a double quantum well heterostructure, fabricated with lateral dimensions of up to about 10 microns, and capable of producing a second electrical signal in proportion to the local magnetic field at the position of said second sensor, and spatially separated from the first magnetic field sensor by a distance of up to about 10 microns;
• and
• a comparator, for receiving and comparing said first and second electrical signals, and for producing an output representing a magnitude of a magnetic field gradient applied across said sensors.