A chip-based C-band ODNP platform

In this paper, we present a chip-based C-band ODNP platform centered around an NMR-on-a-chip transceiver and a printed microwave (MW) Alderman-Grant (AG) coil with a broadband tunable frequency range of 528 MHz. The printable ODNP probe is optimized for a high input-power-to-magnetic-field conversion efficiency, achieving a measured ODNP enhancement factor of -151 at microwave power levels of 33.3 dBm corresponding to 2.1 W. NMR measurements with and without microwave irradiation verify the functionality and the state-of-the-art performance of the proposed ODNP platform. The wide tuning range of the system allows for indirect measurements of the EPR signal of the DNP agent by sweeping the microwave excitation frequency and recording the resulting NMR signal. This feature can, e.g., be used to detect line broadening of the DNP agent. Moreover, we demonstrate experimentally that the wide tuning range of the new ODNP platform can be used to perform multi-tone microwave excitation for further signal enhancement: Using a 10 mM TEMPOL solution, we improved the enhancement by a factor of two.