At the end of the day, the Overhauser effect is a relaxation game. When one spin species is brought out of thermal Boltzmann equilibrium, mutual spin flips with other species will try to reestablish the equilibrium. If the gyromagnetic ratio of the pertubed spin is greater than that of the unpertubed one, the latter can also be brought to a non-equilibrium state, above thermal Boltzmann levels. As such, the polarization and thus signal intensity of a lower gamma nucleus can be increased. This is called hyperpolarization. For nuclei, the quotient of gyromagnetic ratios is never greater than one order of magnitude. If the perturbed spin is an electron spin, however, enhancements of up to three to four orders of magnitude are possible. This is the idea behind Overhauser Dynamic Nuclear Polarization (ODNP). Mutual spin flips require the interaction (i.e. coupling) between the nuclear and electron spin be strong and, importantly, this interaction is modulated at the right frequency. This is why the ODNP mechanism is only active in solution-state where molecules are free to move and collide with one another. If one wishes to perform DNP experiments in the solid-state, different mechanisms (e.g. the aptly called solid-effect) have to be used.

Below are shown a carbon-13 and fluorine-19 spectrum, which have been enhanced using the liquid-state ODNP setup developed in the Bennati group. Although the enhancements one can obtain with ODNP are not as large as other hyperpolarization techniques, one major benefit is that this setup is modular. This means anyone with a 400 MHz instrument can connect a gyrotron to it and perform experiments as usual, just with greater sensitivity, at no cost! (well, ideally) If DNP experiments are not desired, one can simply turn off the gyrotron and perform experiments without microwave irradiation. The probe that is currently in use is a modified version of a commercial dual-channel probe, with mirrors introduced that allow orthogonal microwave irradiation of samples. The microwaves are generated by a 263 GHz gyrotron and are guided to the sample via a corrugated waveguide. A mechanical shutter additionally allows gating of the microwaves. For all details on our setup and its potential, please see our recent publication!