Carbon-based nanoparticles have exhibited unique materials properties and multipurpose usages in nanoscience and biomedicine . In tandem with the characteristics of this important class of nanomaterials , the remarkable optical and magnetic properties of diamond nanoparticles have attracted strong interest in a versatile range of applications , including hyperpolarized magnetic resonance imaging (MRI) and chemical sensing in fluids . Recent studies have been targeted at unraveling dynamic nuclear polarization (DNP) , a process in which saturation or pumping of paramagnetic defects in diamond nanocrystals by microwave fields or optical illumination can generate nuclear spin polarizations order of magnitude larger than thermal equilibrium polarization . All these novel applications depend on the spatial distribution of paramagnetic centers around the core carbon structure of diamond nanoparticles .