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DBL%20Hendrix%20small.png College chemistry, 1983

Derek Lowe The 2002 Model

Dbl%20new%20portrait%20B%26W.png After 10 years of blogging. . .

Derek Lowe, an Arkansan by birth, got his BA from Hendrix College and his PhD in organic chemistry from Duke before spending time in Germany on a Humboldt Fellowship on his post-doc. He's worked for several major pharmaceutical companies since 1989 on drug discovery projects against schizophrenia, Alzheimer's, diabetes, osteoporosis and other diseases. To contact Derek email him directly: Twitter: Dereklowe

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March 12, 2014

A New NMR Probe Technology in the Making?

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Posted by Derek

This paper is outside of my usual reading range, but when I saw the title, the first thing that struck me was "NMR probes". The authors describe a very sensitive way to convert weak radio/microwave signals to an optical readout, with very low noise. And looking over the paper, that's one of the applications they suggest as well, so that's about as far into physics as I'll get today. But the idea looks quite interesting, and if it means that you can get higher sensitivity without having to use cryoprobes and other expensive gear, then speed the day.

Comments (5) + TrackBacks (0) | Category: Analytical Chemistry


1. David Borhani on March 12, 2014 4:30 PM writes...

Very interesting. The response frequency of ~0.7 MHz seems to be about 3 orders of magnitude lower than would be useful in (current high-field) NMR. Mechanical resonant freq. ("drum mode") scales inversely with membrane linear dimension, so a much smaller device would appear to be needed. But, this optoelectromechanical coupling is rather complicated, and I may have that wrong. If much smaller is needed, would sensitivity of the detector then scale unfavorably (I cannot figure out from the paper how it would scale, but one might guess with the area of the detector)?

For NMR signals, we need to detect the carrier (~1 GHz) efficiently, but also (and especially) the kHz-modulation of that carrier (for peak chemical shifts & integration). Linearity & noise become prime concerns, over and above simply detecting the carrier (which seems to be mostly what they’re doing here). With RF coil pickups (NMR probes of today), the electrons pretty much move at whatever frequencies (carrier & chem. shifts) are present in the impinging (signal) electric field. Once mechanical vibration enters the picture, some frequencies are just not going to be in- (or near-) resonance with the fundamental (& harmonic) drum frequencies. It would be like having an audio signal where you apply some narrow band-stop (or notch) filters—just cut out the 200-600 Hz signal, who needs it? Would make the music sound awfully weird (Karaoke?). How good in practice the broad drum freq. response would be I just don’t know.

Bottom line, this stuff is really way beyond me, too. Really complicated E&M/quantum stuff. So I could be just off base. At any rate, it is very cool! Thanks for bringing it to our attention.

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2. SteveM on March 12, 2014 6:45 PM writes...

I spoke with a shrink from NIMH once, and he told me that the real geniuses,(genii?) there were the physicists working behind the curtain on signal processing solutions for the diagnostic platforms.

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3. sepisp on March 13, 2014 4:13 AM writes...

#1: So, essentially, we have an excellent microphone, with the catch that it can only detect one frequency at a narrow range of loudnesses. It is also likely to be very easily damaged by excess power.

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4. David Borhani on March 13, 2014 8:43 AM writes...

@3: I *think* so, but, like I wrote, this is pretty complicated physics, and I may very well be misunderstanding some of it.

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5. a. nonymaus on March 13, 2014 10:22 AM writes...

For NMR, the big issue is coupling the signal from the sample to the detector. Getting this signal from the sample to the membrane seems like it would require the same sample coil, etc. At present, the thermal noise in the coil is the main contributor to the noise floor, which is why there are cryoprobes. This new transducer should pick up thermal noise just as much.

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