# Zero- to ultralow-field J-spectroscopy with a diamond magnetometer

## TL;DR

Researchers developed a compact, portable NMR system using a diamond sensor to detect chemical signals in tiny volumes without needing a strong magnetic field.

## Contribution

The novel integration of diamond-based magnetometry with zero- to ultra-low-field NMR enables chemically specific sensing in microscopic volumes.

## Key findings

- NMR signals at frequencies of a few hertz were detected using a diamond magnetometer.
- The system successfully observed the J-coupling pattern of acetonitrile using SABRE hyperpolarization.
- The sensor achieved high sensitivity with a stand-off distance of less than 1 mm.

## Abstract

Nuclear magnetic resonance (NMR) is a powerful tool for probing molecular structure and dynamics, but conventional high-field systems are bulky and suffer from field inhomogeneities. Zero- to ultra-low-field (ZULF) NMR overcomes these limits by exploiting internal spin interactions in a magnet-free, shielded environment. When combined with nitrogen-vacancy centers in diamond, it enables a compact, portable platform with high spatial resolution and broad bandwidth for noninvasive chemical sensing in microscopic volumes and real-world settings. We report detection of zero- to ultralow-field nuclear magnetic resonance (ZULF NMR) signals at frequencies of a few hertz using a diamond magnetometer. The sensing diamond is a truncated pyramid with 180 μm height and a 5002
μm2 base. The minimum stand-off distance is <1 mm, and the sensor sensitivity is 13 pT/\documentclass[12pt]{minimal}
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\begin{document}$$\sqrt{Hz}$$\end{document}Hz at frequencies f above 5 Hz with 1/f-like behavior at lower frequencies. NMR signals were generated via signal amplification by reversible exchange (SABRE) parahydrogen-based hyperpolarization resulting in zero-field signals at 1.7 Hz and 3.4 Hz corresponding to the expected hetero-nuclear J-coupling pattern of acetonitrile. This work demonstrates a magnet-free platform for detecting chemically specific NMR signals paving the way for portable noninvasive diagnostics in microscopic sample volumes for biomedicine, industrial sensing through metal enclosures.

Zero-to-ultra-low-field nuclear magnetic resonance (ZULF NMR) enables high-resolution spectroscopy of inhomogeneous samples in complex environments. In this work, the authors incorporate a diamond-based magnet sensor to ZULF NMR, reporting the observation of NMR signals corresponding to the hetero-nuclear J-coupling pattern of acetonitrile via signal amplification by reversible exchange (SABRE), demonstrating a magnet-free platform for detecting chemically specific NMR signals at ultra-low frequencies.