We report on EPR and 13C and 1H NMR studies of detonation nanodiamond particles with surface grafted by paramagnetic gadolinium ions obtained by ion exchange with hydrogen atoms of carboxyl groups through the reaction of aqueous nanodiamond suspension with an aqueous solution of gadolinium nitrate. Our findings give clear evidence that Gd3+ ions are chemically bound to the nanodiamond surface and interact with electron and nuclear spins of the diamond nanoparticle, which results in acceleration of electron and nuclear spin-lattice relaxations. A model of positioning of Gd3+ ions on the DND surface terminated by oxygen-containing groups is suggested. The distance between the Gd ion and nanodiamond surface is estimated by relaxation measurements as 0.32 nm. Biomedical applications of the studied nanomaterials are discussed.