Size dependence of physical properties of nanodiamond particles is of crucial importance for various applications in which defect density and location as well as relaxation processes play a significant role. In this work, the impact of defects induced by milling of micron-sized synthetic diamonds was studied by magnetic resonance techniques as a function of the particle size. EPR and (13)C NMR studies of highly purified commercial synthetic micro- and nanodiamonds were done for various fractions separated by sizes. Noticeable acceleration of (13)C nuclear spin-lattice relaxation with decreasing particle size was found. We showed that this effect is caused by the contribution to relaxation coming from the surface paramagnetic centers induced by sample milling. The developed theory of the spin-lattice relaxation for such a case shows good compliance with the experiment.

We report on the first 1H NMR relaxation and magnetic resonance imaging (MRI) study of aqueous suspensions of detonation nanodiamond (DND) grafted by Gd­(III) ions. In contrast to Gd­(III)–ND conjugates implemented via organic species, Gd­(III) ions were directly grafted to the surface of DND particles. Such Gd­(III)-grafted DND particles significantly shorten spin–lattice (T 1) and spin–spin (T 2) relaxation times of water protons providing relaxivities of r 1 = 33.4 and r 2 = 332 mM–1 s–1, which considerably exceed most of those reported in the literature. It makes the Gd­(III)-grafted DND complexes attractive for use as novel MRI contrast agents.

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