A miniaturized dual-mode continuous-wave and pulsed pumping ODNP platform

In this paper, we present the design and experimental validation of a miniaturized Overhauser dynamic nuclear polarization (ODNP) platform for both continuous-wave (CW) and pulsed DNP enhancement experiments at a $B_0$ field strength of 0.25 T. The platform is centered around chip-integrated nuclear magnetic resonance (NMR) and microwave (MW) electronics and further incorporates a custom-designed laser-engraved ODNP probe, providing phase-coherent radio frequency (RF) excitation, low-noise amplification and acquisition of NMR signals, MW frequency synthesis, MW signal modulation, and MW power amplification. An experimental validation using TEMPOL solutions with different concentrations demonstrates the functionality and good performance of the presented ODNP platform. A maximum enhancement of $-92$ with CW pumping was achieved using a 500 nL 10 mM non-degassed TEMPOL solution in water, representing the largest enhancement achieved to date in a chip-based ODNP platform. We also include a preliminary comparison between CW pumping and pulsed pumping using TEMPOL solutions with different electron relaxation times (apparent $T_{{1e}^{\ast }}$ and $T_{\mathrm{2e}}$). Our study indicates that, for a power-limited miniaturized ODNP platform, pulsed pumping can surpass CW pumping in power efficiency for a given average power when the solution possesses a sufficiently long electron spin-lattice relaxation time.