NMR-on-a-Chip Devised

A supersensitive minisensor can detect nuclear magnetic resonance (NMR) in tiny liquid samples flowing through a novel microchip. The prototype device, which combines an atomic magnetometer with a fluid channel, could be used to rapidly screen for new drugs, or to track fluid or gas flow for industrial processes and oil exploration.

The "nuclear magnetic resonance on a chip" device was developed at the National Institute of Standards and Technology (NIST) in collaboration with the University of California at Berkeley. In experiments, it was able to detect magnetic signals from atomic nuclei in tap water flowing through a tiny fluid channel on a custom silicon chip.

The Berkeley group recently co-developed this "remote NMR" technique for tracking small volumes of fluid or gas flow inside soft materials such as biological tissue or porous rock for industrial and oil exploration applications. The chip could also be used in NMR spectroscopy, a widely used technique for determining physical, chemical, electronic and structural information about molecules. NMR signals are equivalent to those detected in MRI (magnetic resonance imaging) systems.

Prototype microchip device combines the National Institute of Standards and Technology's miniature atomic magnetometer with a fluid channel for studying tiny samples. (Image courtesy NIST)

Berkeley scientists selected the NIST sensor, a type of atomic magnetometer and a spinoff of its tiny atomic clocks, for the chip device because of its small size and high sensitivity, which make it possible to detect weak magnetic resonance signals from a small sample of atoms in the adjacent microchannel. The minisensor has also been shown to have biomedical imaging applications.

Detection is most efficient when the sensor and sample are about the same size and located close together, said Micah Ledbetter, lead author of a paper on the research, making a small sensor crucial for working with small samples.

Its small size and extreme sensitivity make the NIST sensor ideal for the microchip device, in contrast to SQUIDs (superconducting quantum interference devices) that require bulky equipment for cooling to cryogenic temperatures or conventional copper coils that need much higher magnetic fields (typically generated by large, superconducting magnets) like those in traditional MRI, the researchers said. A joint university/NIST patent application is being filed for the device.

The principal investigator for the study, published this month in the Proceedings of the National Academy of Sciences (PNAS), is Alexander Pines, a leading authority on NMR. The research was supported by the Office of Naval Research, US Department of Energy, a California Space Institute (CalSpace) minigrant and DARPA.

For more information, visit: www.nist.gov