High magnetic moment particle detection

1. A device comprising:

a sensor having a surface, the surface including a plurality of conductive layers interspersed by a plurality of intermediary layers, a magnetization direction of a first subset of the plurality of conductive layers and a magnetization direction of a second subset of the plurality of conductive layers having a ground state orientation of approximately 0 degrees, wherein the first subset is exclusive of the second subset; and

a pair of electrodes coupled to the sensor surface and wherein an electrical resistance difference between the pair of electrodes is determined by a magnetic field proximate the sensor surface and wherein the sensor surface has an aspect ratio, corresponding to a length and a width of the sensor surface, that is sufficiently small such that a magnetic dipole field of a nanoparticle proximate the sensor surface is detectable as an electrical resistance difference between the pair of electrodes.

2. The device of claim 1 wherein the sensor surface includes voids or inclusions configured to form a multidomain structure.

3. The device of claim 1 wherein the sensor surface is configured to detect proximity of a high magnetic moment nanoparticle.

4. The device of claim 1 wherein the ground state orienation is less than 60 degrees.

5. The device of claim 1 wherein the nanoparticle has a magnetic moment greater than 100 emu/g at room temperature.

6. The device of claim 1 wherein the nanoparticle has a magnetic moment that is seven times greater than that of magnetic oxide nanoparticles at 10 Oe magnetic field.

7. The device of claim 1 wherein the nanoparticie includes high magnetic moment FeCo nanoparticle.

8. The device of claim 7 wherein the nanoparticle is approximately 12 nm.

9. The device claim 1 wherein the sensor surface and the pair of electrodes are integrated in a chip.

10. The device of claim 9 wherein the chip includes a processor module configured to acquire data corresponding to the magnetic field.

11. The device of claim 1 further including a magnetic field generator module configured to generate the magnetic field.

12. The device of claim 11 wherein the magnetic field generator module is configured to generate two or more fields having a frequency in the range of 0 Hz to 1 MHz.

13. The device of claim 1 wherein the magnetic field is determined by a ratio of magnetic particle tagged binding partners to untagged binding partners.

14. The device of claim 1 wherein the sensor surface has a width of approximately 40 μm and a length of approximately 80 μm.

15. The device of claim 1 wherein the sensor surface has a ratio of length to width of less than 100.

16. The device of claim 1 wherein the sensor has a non-zero coercivity force.

17. The device of claim 1 wherein the electrical resistance as a function of the magnetic field exhibits hysteresis.

18. The device of claim 1 wherein the sensor surface includes at least one microfluidic channel.

19. The device of claim 1 wherein the sensor surface includes a container configured to receive a fluid sample.

20. The device of claim 1 wherein the sensor surface is part of at least one of a giant magnetoresistive (GMR) sensor, a magnetic tunneling junction (MTJ) sensor, an anisotropic magnetic (AMR) sensor, a giant magneto inductance (GMI) sensor, a Hall magnetic sensor, a magneto-optical sensor, or other sensor that provides an electrical output based on a change in magnetic field.

21. The device of claim 1 further including an interface to exchange data based on the electrical resistance with a remote device.

22. The device of claim 1 further including a notch in a perimeter of at least one conductive layer, the notch configured to pin the magnetization.