Abstract
Low thermal-equilibrium nuclear spin polarizations and the need for sophisticated instrumentation render conventional nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI) incompatible with small-scale microfluidic devices. Hyperpolarized 129Xe gas has found use in the study of many materials but has required very large and expensive instrumentation. Recently a microfabricated device with modest instrumentation demonstrated all-optical hyperpolarization and detection of 129Xe gas. This device was limited by 129Xe polarizations less than 1%, 129Xe NMR signals smaller than 20 nT, and transport of hyperpolarized 129Xe over millimeter lengths. Higher polarizations, versatile detection schemes, and flow of 129Xe over larger distances are desirable for wider applications. Here we demonstrate an ultra-sensitive microfabricated platform that achieves 129Xe polarizations reaching 7%, NMR signals exceeding 1 μT, lifetimes up to 6 s, and simultaneous two-mode detection, consisting of a high-sensitivity in situ channel with signal-to-noise of 105 and a lower-sensitivity ex situ detection channel which may be useful in a wider variety of conditions. 129Xe is hyperpolarized and detected in locations more than 1 cm apart. Our versatile device is an optimal platform for microfluidic magnetic resonance in particular, but equally attractive for wider nuclear spin applications benefitting from ultra-sensitive detection, long coherences, and simple instrumentation.
Highlights
The devices are fabricated by etching holes and grooves from a silicon wafer and bonding glass windows to both sides of the silicon, forming a series of chambers and channels. 129Xe flows into the device and is polarized through spin-exchange optical pumping (SEOP)[5] with Rb vapor polarized using a distributed feedback (DFB) laser
The polarized 129Xe flows through a 1 cm microfluidic channel, experiences magnetic field pulses, and is optically detected using Rb vapor and another DFB laser configured to operate as a zero-field magnetometer
We have presented a microdevice composed of glass and silicon which is capable of optically producing and detecting hyperpolarized 129Xe gas for use in magnetic resonance experiments
Summary
Coupling 129Xe with AVAMs is attractive because similar instrumentation is used for both polarization and detection and AVAMs are inherently more sensitive than inductive detectors at the low-to-moderate fields required for efficient 129Xe hyperpolarization, especially for very small device sizes[18] This allows both in situ and ex situ detection modalities for a wide range of applications and operating conditions while using simple optical technologies. We find that in situ detection provides a signal enhancement by a factor between 2000 and 5000, depending on device geometry These results demonstrate that 129Xe can be efficiently polarized and detected in a wide range of conditions using an integrated single-chip platform. When combined with methodological developments in microfluidic remote detection NMR24, these results should greatly improve the prospects for the use of fully integrated 129Xe NMR instrumentation in small, portable, inexpensive microfluidic devices
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