We used a home-built ZULF spectrometer for signal detection which is a modified version of the setup described in reference . Using a four-layer µ-metal shield (MS-1, Twinleaf LCC) and additional shimming coils, the residual field at the sample location was brought down to sub-nT levels. At the center of the detection region, a 3D-printed holder accommodated a standard NMR tube and a Helmholtz-coil pair along the sensitive axis (z-axis). The ZULF spectrometer was equipped with a solenoid coil to guide the sample from the prepolarization magnet to the Helmholtz coils during experiments without hyperpolarization. In the context of hyperpolarized experiments, the output of the d DNP polarizer was connected to the NMR tube inside the ZULF spectrometer via the prepolarization magnet and the guiding solenoid. A magnetic tunnel consisting of copper wire wound directly around the transfer capillary and fed with a current of 2 A provided a field of 4 mT along the transfer.