A super-sensitive mini-sensor developed at the National
Institute of Standards and Technology (NIST)
can detect nuclear magnetic resonance (NMR) in tiny samples of fluids
flowing through a novel microchip. The prototype chip device, developed
in a collaboration between NIST and the University of California, may
have wide application as a sensitive chemical analyzer, for example in
rapid screening to find new drugs.
As described in Proceedings of the National Academy of
Sciences (PNAS),* the NMR chip detected magnetic signals from atomic
nuclei in tap water flowing through a custom silicon chip that
juxtaposes a tiny fluid channel and the NIST sensor. 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 possible applications in
industrial processes and oil exploration. The chip could 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
Berkeley scientists selected the NIST sensor, a type of atomic
magnetometer, 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.
Detection is most efficient when the sensor and sample are about the
same size and located close together, lead author Micah Ledbetter says.
Thus, when samples are minute, as in economical screening of many
chemicals, a small sensor is crucial, Ledbetter says.
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 results reported in the PNAS demonstrate another use for
the NIST mini-sensor, a spin-off of NIST’s miniature atomic
clocks. The sensor already has been shown to have biomedical imaging