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Pines and colleagues enhance NMR/MRI signals to track gases and liquids in microfluidic devices

Alex Pines
Alex Pines

January 28, 2008

Although he is a classical music lover, chemistry professor Alex Pines admits to a begrudging respect for Jimi Hendrix. “Hendrix started with the guitar string and amplified its signal to make it very loud, but in a way that was, well, interesting,” says Pines. “I start with molecules, and amplify their NMR signals, making them louder in a way that chemists find interesting.”

As reported in a recent Science magazine (25 Jan 2008) article, Pines and colleagues at the Lawrence Berkeley National Laboratory (LNBL) used enhanced nuclear magnetic resonance (NMR) to help improve the design of future catalysts and catalytic reactors, especially microfluidic “lab-on-a-chip” devices.

NMR has been likened to the plucking of a guitar string. When the tensioned string is struck by the force of a finger tip, it resonates with a characteristic frequency. Likewise, when held in tension by extremely powerful electromagnet fields, and struck by a pulse of radio-frequency energy, certain molecules resonate with a characteristic radio-frequency signature.

Pines and colleagues have devised a way to amplify NMR signals so that they can detect molecular signals from minute samples and trace their movement in real time inside catalytic reactors and microfluidic devices.

NMR signals are made possible by a property found in the atomic nuclei of almost all molecules called “spin,” which gives rise to a magnetic moment, meaning the nuclei act as if they were bar magnets with a north and south pole. Obtaining an NMR signal depends on the nuclei having a disproportionate amount of one type of spin over the other—otherwise the result is noise.

The Pines team developed a technique in which they first polarized hydrogen gas, magnetically aligning as many hydrogen atoms as possible. Next they used this gas to form more gaseous products that maintained the magnetic properties of the hydrogen. These magnetically polarized gases yield a much stronger NMR signal than their non-polarized versions, akin to the impact of several guitarists striking the same chord simultaneously, instead of different chords at random times.

These polarized gases are then processed in catalytic reactors and microfluidic devices, where they enhance their NMR signal to the point that these gases and liquids can be traced as they move through microfluidic devices and catalytic reactors.

Since nearly all manufacturing processes that involve chemistry start with a catalytic reaction, there is a premium on the design of new and better catalysts and catalytic reactors. This is especially true for the growing field of microfluidic chip technology.

The costs of researching and developing new catalysts can be very expensive, and the parahydrogen-enhanced MRI/NMR technique developed by Pines and his collaborators has the potential to significantly reduce these costs, as well as substantially speed up the process.

Not only does it allow future studies of potential catalysts to be carried out on a smaller and more economical scale, it is also well-suited for “green chemistry,” the new approach that seeks to maximize productivity and yield while minimizing costs, amounts of reactants and waste products.

More Information

LBNL Research News Article: Berkeley Scientists Bring MRI/NMR to Microreactors
College of Chemistry Faculty Web Page

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