Zero- to Low-field Relaxometry of Chemical and Biological Fluids

NMR relaxometry is an analytical method that provides information about the molecular environment, including even NMR “silent” molecules (spin-0), by analyzing the properties of NMR signals versus the magnitude of the longitudinal field. Conventionally, this technique has been performed at fields much higher than Earth’s magnetic field, but in this work, we present NMR relaxometry at zero and ultra-low magnetic fields (ZULFs). Operation under ZULFs allows us to investigate many slow (bio)chemical processes, whose timescale (milliseconds-seconds) coincides with a timescale of spin evolution. ZULFs regime also limits the detrimental role of T2 dephasing, which, in heterogeneous samples, is induced by magnetic susceptibility and often leads to line broadening, hence low-resolution spectra. Finally, in contrast to their high-field NMR, ZULF NMR measurements can be performed with inexpensive, portable/small-size sensors (atomic magnetometers). Here, we use ZULF NMR relaxometry in the analysis of (bio)chemical compounds containing 1H 13C, 1H-15N, and 1H-31P spin pairs. We also detected high-quality ULF NMR spectra of human whole blood at 0.8 μT, despite a shortening of spin relaxation by blood proteomes (e.g., hemoglobin). Information on relaxation times of blood, a potential early biomarker of inflammation, can be obtained in less than a minute and without the need for a sophisticated apparatus.