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

Abstract Nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical tool of modern science and technology. Apart from rich information that can be extracted from the frequencies of precessing nuclear spins, detection of the decay of the signals (NMR relaxometry) may reveal important information about molecular environment, including NMR-silent (spin-0) molecules. While conventionally done at high fields, in this work, we present NMR relaxometry at zero and ultra-low magnetic field (ZULF) regime. Operation under these conditions is especially promising because spin evolution occurs at timescales (milliseconds to seconds) comparable to those of many slow (bio)chemical processes allowing their investigation. It also limits the detrimental role of line-broadening induced by magnetic susceptibility. These measurements can be performed with an inexpensive, portable/small-size system. Applicability of the ZULF NMR relaxometry is demonstrated in analysis of various (bio)chemicals including 1H-13C, 1H-15N, and 1H-31P spin systems. We observed high-quality ZULF NMR spectra of human whole blood, despite a shortening of spin relaxation time of its water protons (0.3-0.4 s) induced by blood proteomes (e.g., hemoglobin). The information about the relaxation times of blood and, potentially, other biofluids, can be obtained with sample preparation in less than a minute and without the need for a sophisticated apparatus.