<p dir="ltr">We report measurements of zero- to ultra-low-field nuclear magnetic resonance (ZULF NMR) sig- nals at frequencies of a few hertz with a diamond-based magnetic sensor. 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/√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 demon- strates a magnet-free platform for detecting chemically specific NMR signals at ultra-low frequencies paving the way for portable noninvasive diagnostics in microscopic sample volumes for biomedicine, industrial sensing through metal enclosures, and field-deployable quantum analytical devices.</p>
