Proton magnetic resonance study of diamond nanoparticles decorated by transition metal ions

We report on a ¹H NMR study of diamond nanoparticles decorated by copper and cobalt. Increase in the ¹H relaxation rate under decoration results from the interactions of hydrogen nuclear spins of the surface hydrocarbon and hydroxyl groups with paramagnetic copper and cobalt ions. This finding reveals the appearance of paramagnetic Cu²⁺ or Co²⁺ ions on the detonation nanodiamond (DND) surface rather than as a separate phase, which is consistent with the ¹³C NMR data of the same samples. Our results shed light on the mechanism of ion incorporation. A topological model for relative position of paramagnetic Cu²⁺ or Co²⁺ ions and hydrogen atoms on the DND surface is suggested. An application of the studied nanomaterials in the field of biomedicine is discussed.