From microwave irradiation of free radicals to cancer imaging and drug screening

by Geoffrey Bodenhausen (Laboratory of Biomolecules at ENS)

For what type of applications is it worthwhile to amplify NMR signals by
dynamic nuclear polarization (DNP)?

Currently, DNP comes in two flavours: (i) in combination with rapid
dissolution to convert a sample that has been hyperpolarized at temperatures in the vicinity of 1 K, so that it can be injected into a solution or into a living being at room temperature, or (ii) in combination with magic-angle spinning (MAS-DNP) to enhance weak signals in solid-state NMR.

The first strategy, initially proposed for monitoring metabolic processes in vivo that are often accelerated in cancerous tissues, has also been used successfully for drug screening in vitro. 
The second strategy has been applied not only to enhance signals of biomolecules and their complexes such as the ribosome, but also to characterize surfaces of porous materials.
Both strategies rely on microwave irradiation to saturate the transitions of electron spins of free radicals in order to enhance the population differences across the transitions of nuclear spins.