The 1-mm Triple-Resonance, High-Temperature Superconducting Probe

This probe is used with our 600 MHz NMR magnet, located at our Advanced Magnetic Resonance Imaging and Spectroscopy program at the lab's University of Florida campus.

Though powerful, this commercially-made 14.1 tesla research magnet is not unique. However, when used with the unique probe developed by the MagLab in cooperation with Bruker Biospin, a company that makes research equipment, this instrument is more than special: It delivers the highest mass sensitivity of any probe at any frequency in the world.

The probe contains a device called a radio frequency (RF) coil, which interacts with the magnet's field and atoms in the sample, sending information about what the sample is made of to a computer.

This particular probe, as you can see from the photos, is quite small – the tube inside it containing the sample is a single millimeter wide. This feat of engineering took years to complete, from conception to end product. Its size is an advantage when you have just a smidgeon of sample, sometimes the case when working, for example, with plant or animal materials. As long as your sample is highly soluble, you can find a wealth of information in a drop of liquid.

In one interesting application, MagLab scientists are studying the venom of the walking stick, promising research that could lead to better cancer drugs. In an early study from the 1960s, researchers milked 1,000 of these insects before accumulating enough venom for an analysis. Today, with this probe, a single milking would do the trick.

The coils in this Nuclear Magnetic Resonance (NMR) probe are made from a superconducting metal oxide. The material is too brittle to bend. Instead, the oxide is deposited on the surface of a crystal and then etched into the right shape – like a microchip. "It's a completely different technology than we normally use, much more complex and expensive," says probe designer Bill Brey. "It took several years to get it to work."

Eventually, of course, they succeeded, and the reward was better data. The probe has been a hit with biologists who have only a tiny amount of the unknown chemical they need to analyze.

This probe's sensitivity is due not only to its small RF coil, but also to the fact that that coil is superconducting. When the coil is cooled to -424 degrees Fahrenheit, or -253 degrees Celsius, current runs through it much more efficiently than in more familiar metal conductors. As a result, it can pick up and pass along the signal from the sample much more effectively. Also, cooling the coil's electronics reduces background noise that might otherwise interfere with the sample's signal. (This probe, by the way, picks up signals from hydrogen, nitrogen-15 and carbon-13 atoms, hence the name triple resonance probe.)

The analogy of a phone line helps illustrate this. If you have a bad connection, you can do one of two things to make the signal come across more clearly: Talk louder or reduce that irksome static. Cooling the electronics reduces the noise, and using the small, superconductive coil increases the signal. Either way (or both), you get a more efficient amplification of the same sound – just as a superconducting coil and/or a smaller coil give you a better NMR signal.

Superconducting materials are used in some other NMR probes to achieve high sensitivity, but never for such small samples. This was also the first superconductive triple resonance probe capable of using interactions between carbon, nitrogen and hydrogen atoms to trace complex structures in proteins.

Finally, this instrument boasts high homogeneity – meaning that the field strength remains very even, at 14.1 tesla, throughout the experimental space.

More Probes

• The Magic Angle Spinning Probe
• The Low-E Probe
• The Rodent Probe

Related Links

For the general public:
• Magnets from Mini to Mighty
• Superconductivity: Current in a Cape and Thermal Tights
• What's a Superconducting Magnet?

For scientists:
• Advanced Magnetic Resonance Imaging and Spectroscopy Program
• Design, construction, and validation of a 1-mm triple-resonance high-temperature superconducting probe for NMR, Journal of Magnetic Resonance, 179 (2006), 290–293.
• Instrument Development for the NMR User Program