Spatially Resolved Spin–Lattice Relaxation Times and Line Widths in Manganese-Grafted Detonation Nanodiamonds

Abstract

We report on a novel approach that allows determining the spatially resolved nuclear spin−lattice relaxation times and NMR line widths in nanomaterials. The approach was applied to a newly synthesized nanomaterialdetonation nanodiamonds with manganese ions directly grafted to the surface of the nanodiamond particles. The interaction of the carbon nuclear spins with paramagnetic Mn 2+ ions results in acceleration of nuclear spin−lattice relaxation and broadening of the 13 C resonance line. Using spin dephasing experiments, we were able to determine the layer-by-layer contributions of the paramagnetic Mn 2+ ions to the spin− lattice relaxation time and line width of the carbon spins positioned at different depths from the diamond surface. Developed for nanodiamonds, this approach is more general and can be successfully applied to study the distribution of nuclear relaxation rates and line broadening and for mapping magnetic interactions inside various nanoparticles, being of practical use in various nanotechnologies.

Universal Dependence of Nuclear Spin Relaxation on the Concentration of Paramagnetic Centers in Nano- and Microdiamonds

“…, which is characteristic of the spin-lattice relaxation through paramagnetic defects [12][13][14][15]19,20,[26][27][28][29][30][31]35]. Here, M ∞ is the equilibrium magnetization, and the parameter α varies in the range of 0.5 < α < 1.…”

“…Similar dependences of the nuclear spin relaxation in nanodiamonds on the concentration of the paramagnetic ions were obtained in our measurements of powder samples. In this case, the spin-lattice relaxation rate R 1 = 1 T 1 of the nuclear spin I, which interacts with the unpaired electron spin S of the paramagnetic ion, is given by the expression [14,15,19,20,22,29…”

“…Detonation nanodiamond (DND) particles are of significant scientific interest and are very promising materials for modern science and applications in quantum computing, spintronics, nanophotonics, and biomedical applications due to the small size of primary particles (5 nm) with a narrow size distribution, easy surface functionalization, high biocompatibility, and possibility of production in large quantities [1][2][3][4][5][6][7][8][9][10][11]. DND suspensions with grafted paramagnetic metal cations [12][13][14][15][16][17][18][19][20] exhibit a high relaxivity and are proposed as new contrast agents for magnetic resonance imaging (MRI) [16][17][18]20]. Recently, Sękowska et al reported the possible use of DNDs in MRI phantoms [21] produced using distilled water, agar, and carrageenan with the addition of the DND particles suspended in dimethyl sulfoxide (DMSO).…”