Uniform field to measure nanoparticles in the blood?

[williamyin08]

I am hoping to build a small and cost-effective magnetic device that can be applied to the neck to measure the presence of a small amount of magnetite nanoparticles in the bloodstream (on the order of 0.0002 to 0.002 um^3). I've looked at using permanent magnets and Helmholtz coils; however, those tend to be very pricey and are more powerful than is necessary. Is there a more effective solution?

Magnetic engineering isn't my forte so I apologize if some of my terminology or conjectures are incorrect.

 

[IRstuff]

And what physical principle are you invoking to make this measurement?

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[williamyin08]

I hope to utilize Nuclear Magnetic Resonance to detect the relaxation rates of nanoparticles and/or of the RF dynamics of protons in water, as outlined in the paper "CMOS RF Biosensor Utilizing Nuclear Magnetic Resonance".

 

[IRstuff]

Am I reading the same paper (IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 44, NO. 5, MAY 2009)? That system works because the 5 microliter sample is being put INSIDE the magnet. For a human neck, therefore, one would expect the magnet to be on the order of at least 15 ft across.

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[williamyin08]

Yes, that's what I had thought; trying to work with that system might not be the best idea. However, there are other papers (such as Lab on a Chip, Issue 13, 2011: "Miniature magnetic resonance system for point-of-care diagnostics") that utilize not the protons in water, but the relaxation time of the samples when labeled with magnetic nanoparticles. Would using a similar technology with the human neck be effective?

 

[MagBen]

are you nanoparticles samll enough to be super-paramagnetic? if yes, the particles can be imaged using MRI. In application for magnetic hyperthermia treatments of cancer, nanoparticles are monitored via MRI.

 

[IRstuff]

@Magben: MRI (magnetic resonsance imaging) is the PC name for nuclear magnetic resonance imaging. That occurred about 30-odd years ago, because people were too scared of the "N" in "NMRI" to get the imaging done, so some clever marketing guy realized that dropping the "N" would make everything much "safer."

@williamyin08: Are you even reading these articles that you keep citing (without links, BTW)? Both cited articles talk about doing NMR on tiny samples. A human neck is literally a hundred times larger than the samples these systems are intended to test. The smallest MRI capable of reading an human neck, in-situ, is about the size of a half-height refrigerator.

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[williamyin08]

@MagBen: Yes, I will be using Fe3O4 magnetite nanoparticles with are superparamagnetic. However, I am not trying to image the nanoparticles; I hope to only detect their presence using a compact magnetic biosensor.

@IRstuff: That was my mistake. I meant to say that I will be using the device to measure the nanoparticles in a specific spot in the carotid artery in the neck, where the 'sample' volume would be between 25 and 75uL. (The paper I cited above states a sample volume of between 1 and 100uL.) Obviously attempting to test within the entirety of the human neck would be close to impossible.

 

[IRstuff]

I think you're missing the point of how the MRI works, the sample needs to be completely immersed in the magnetic field, which means from ALL sides, which cannot be done on an individual artery.

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[MagBen]

But your superparamag particles will not respond to a permanent magnet, or a DC magnetic field.
Also, even if your particles are ferromagnetic, I can not imagine how Helmholtz coils could detect the presence of particles. The particles themselves present no magnetic field to be detected if without a presence of an external field. Note Helmholtz coils do not generate a magnetic field.

 

[IRstuff]

The magnet itself is only part of the process. The rest generates an alternating field that flips the spin of the particles, which, in turn, results in generating, an RF signal which can be detected and decoded.

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[EdStainless]

Using a coil pair to produce a region of uniform field was the project that Helholtz was working on, so it works both ways. I have seen Hh coils being driven with both DC and AC simultaneously for testing devices.

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[MagBen]

Ed, you are right on using HZ coils to genreate a field as long as you apply a current in the coils. what I meant was to use Hh coils along a meter to measure flux or flux density without applying a current. sorry for confusion.

 

[EdStainless]

MB, I thought that was what you meant, I am glad that we both commented for clarity.

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