In this experiment, performed at the University of California at Berkeley, we demonstrate remote detection of nuclear magnetic resonance (NMR) with a microchip-like sensor consisting of a microfluidic channel and a microfabricated vapor cell (the heart of an atomic magnetometer). Detection occurs at zero magnetic field, which allows operation of the magnetometer in the spin-exchange relaxation-free (SERF) regime and increases the proximity of sensor and sampleby elimi-nating the need for a solenoid to create a leading field.

The experimental setup is shown in Figure 1. Tap water flows though  800 μm inner diameter teflon tubes from a reservoir in a prepolarizing field to an encoding region, and finally through the microchip housed in a 4-layer set of magnetic shields. In the first experiment, we achieved NMR linewidth of 31 Hz, limited, we believe, by the residence period in the encoding region. In a fully optimized system, we estimate that for 1 second of integration, 7 x 1013 protons in a volume of 1 mm3, prepolarized in a 10 kG field, can be detected with a signal- to-noise ratio of about 3.

In a second experiment, we used a slightly improved version of this system to demonstrate direct detection of J-spectra due to both heteronuclear and homonuclear J-coupling in a zero-field environment where the Zeeman interaction is completely absent.  Scalar couplings of the form JI1∙I2 between nuclei impart valuable information about molecular structure to nuclear magnetic-resonance spectra. We show that characteristic functional groups exhibit distinct spectra with straightforward interpretation for chemical identification. Detection is performed with a microfabricated optical atomic magnetometer, providing high sensitivity to samples of microliter volumes. We obtain 0.1 Hz linewidths and measure scalar-coupling parameters with 4 mHz statistical uncertainty. We anticipate that the technique described here will provide a new modality for high-precision “J spectroscopy” using small samples on microchip devices for multiplexed screening, assaying, and sample identification in chemistry and biomedicine.

Contact: Micah Ledbetter, UC Berkeley


M.P. Ledbetter, I.M. Savukov, D. Budker, V. Shah, S. Knappe, J. Kitching, D. Michalak, S. Xu, and A. Pines, Zero-field remote detection of NMR with a microfabricated atomic magnetometer, Proc. Natl. Acad. Sci. U.S.A., 105, 2286-2290 (2008).

M.P. Ledbetter, C.W. Crawford, A. Pines, D.E. Wemmer, S. Knappe. J. Kitching, and D. Budker, Optical detection of scalar coupling at zero magnetic field, J. Magn. Reson., accepted.


This work was carried out in collaboration with the groups of Dima Budker and Alex Pines at UC Berkeley.


Dima’s lab

Alex’s lab

Fig. 1. Experimental setup. Water flows from a reservoir inside a 7-kG permanent magnet through the encoding region where there is a Helmholtz coil used to apply AF ( ≈ 1 kHz) pulses. The water subsequently flows into a channel with dimensions ≈ 1×2×3 mm3 adjacent to a microfabricated atomic magnetometer vapor cell containing Cs and 5000 torr of N2. Insets hows a photograph of the chip before the ITO heaters were installed.

Experimental and simulated zero-field NMR spectra for ethanol 1, 12CH3-13CH2- OH. To the extent that signal is above the noise level, experiment and simulation are in agreement. The positions of the multiplets are determined by the heteronuclear J-coupling and the splittings within the multiplets are due to homonuclear J-coupling and higher-order effects of heteronuclear J-coupling.