Detection of J-coupling using atomic magnetometer
Inventors
Ledbetter, Micah P. • Crawford, Charles W. • Wemmer, David E. • Pines, Alexander • Knappe, Svenja • Kitching, John • Budker, Dmitry
Assignees
National Institute of Standards and Technology NIST • University of California San Diego UCSD
Publication Number
US-9140657-B2
Publication Date
2015-09-22
Expiration Date
2030-04-13
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Abstract
An embodiment of a method of detecting a J-coupling includes providing a polarized analyte adjacent to a vapor cell of an atomic magnetometer; and measuring one or more J-coupling parameters using the atomic magnetometer. According to an embodiment, measuring the one or more J-coupling parameters includes detecting a magnetic field created by the polarized analyte as the magnetic field evolves under a J-coupling interaction.
Core Innovation
The invention provides a method of detecting J-coupling by positioning a polarized analyte adjacent to a vapor cell of an atomic magnetometer and measuring one or more J-coupling parameters using the atomic magnetometer. This measurement includes detecting the magnetic field created by the polarized analyte as it evolves under a J-coupling interaction.
The invention addresses the problem that conventional nuclear magnetic resonance (NMR) methods require large, immobile, and expensive superconducting magnets to generate high magnetic fields. Low-field and zero-field NMR have attracted attention because they eliminate the need for superconducting magnets, but typically suffer from low sensitivity, low nuclear spin polarization, and poor signal-to-noise ratio when using inductive detection methods at low frequencies. Existing low-field NMR lacks site-specific chemical shifts and generally has lower sensitivity compared to high-field NMR. This invention aims to provide a high-sensitivity detection technique for J-coupling parameters at zero or low magnetic fields without the drawbacks of conventional methods.
The invention utilizes a microfabricated optical atomic magnetometer housed within magnetic shields to operate in a zero or near-zero magnetic field, achieving high absolute field homogeneity and temporal stability. This allows the acquisition of J-coupling spectra with linewidths as low as 0.1 Hz and scalar coupling parameters measured with a statistical uncertainty of 4 mHz. The method involves polarizing the analyte in a strong magnetic field and then moving it to a zero field detection volume adjacent to the vapor cell, where magnetic field pulses prepare a superposition of eigenstates of the J-coupling Hamiltonian. The magnetic field generated by the evolution of these eigenstates under J-coupling is directly detected using the atomic magnetometer, enabling simplified, high-resolution “J spectroscopy” for chemical and biomedical applications without the need for superconducting magnets.
Claims Coverage
The patent contains one independent claim outlining a method for detecting J-coupling. The main inventive features focus on the arrangement of the polarized analyte, application of magnetic pulses, and detection using an atomic magnetometer in a controlled magnetic environment.
Detection of J-coupling using an atomic magnetometer in a magnetically shielded environment
This feature covers providing an analyte in a detector cell adjacent to a vapor cell of an atomic magnetometer, where both cells are housed within a magnetic shield isolating them in a static magnetic field.
Application of a magnetic field pulse to the analyte
This feature includes applying a magnetic field pulse to the analyte in the detector cell to induce magnetization evolution under one or more J-coupling interactions.
Detection of magnetic field generated by analyte magnetization evolution
This covers detecting the magnetic field generated by the analyte using the atomic magnetometer as the magnetization evolves due to one or more J-coupling interactions.
Polarization and transport of analyte prior to detection
The analyte is polarized before detection through techniques such as thermalization in a strong magnetic field, spin-exchange optical pumping, parahydrogen induced polarization, or dynamic nuclear polarization. Additionally, the analyte may be transported to the detector cell.
Operating in low or near-zero static magnetic fields
The method operates within a static magnetic field with magnitude less than about 2.5 nanotesla or up to about 1 millitesla, ensuring a Larmor precession frequency of the analyte less than about 100 mHz.
Magnetic field pulse application using coils within magnetic shield
A pulse of DC current applied to coils positioned within the magnetic shield generates the magnetic field pulse used for exciting the analyte spins to create J-coupling evolution.
The independent claim defines a method for detecting J-coupling by providing a polarized analyte adjacent to an atomic magnetometer vapor cell within a magnetically shielded static field, applying magnetic field pulses to induce J-coupling evolution, and detecting the resulting magnetic field with the atomic magnetometer. Additional features include analyte polarization methods, analyte transport, operating at low or zero magnetic fields, and controlled magnetic pulse application using coils within the shield.
Stated Advantages
Elimination of superconducting magnets by enabling NMR detection at low and zero magnetic fields.
High sensitivity detection of scalar couplings due to direct magnetic field sensing by atomic magnetometers rather than inductive detection.
Capability to achieve narrow linewidths (~0.1 Hz) and precise measurement of scalar coupling parameters with very low statistical uncertainty (4 mHz).
Simplified spectral interpretation in zero field with retention of key analytical information for molecular structure identification.
Operation in a highly homogeneous and temporally stable zero field environment reduces spectral complexity and noise.
Portability and miniaturization are enabled by small vapor cells and elimination of cryogenics as required by SQUID magnetometers.
Ability to perform high-resolution J spectroscopy on microliter-scale samples, suitable for multiplexed screening and biochemical assays.
Documented Applications
Analytical chemistry for precise identification of chemical species and molecular structure elucidation based on J-coupling spectra.
Monitoring chemical reactions, including enzyme-catalyzed reactions and catalyst performance by detecting changes in scalar couplings.
Pharmaceutical industry applications for drug discovery by assessing whether a drug molecule has bound to its receptor through changes in J-coupling.
Chemical production facilities for real-time monitoring of reactants, products, and by-products to optimize process parameters.
Security screening applications, such as airport screening machines, to detect liquid explosives by recognizing characteristic J-coupling spectra.
Detection of parahydrogen induced polarization (PHIP) signals for magnetization enhancements in zero field nuclear magnetic resonance spectroscopy without the use of magnets.
Portable sensors for chemical analysis and imaging utilizing zero-field NMR techniques enhanced by atomic magnetometers and PHIP.
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