Examining relaxivities in suspensions of nanodiamonds grafted by magnetic entities: comparison of two approaches

Objectives: Detonation nanodiamonds (DND) with Gd³⁺ ions directly grafted to the DND surface have recently demonstrated enhanced relaxivity for protons in aqueous suspensions. Herewith, the relaxivity measurements were done on a series of suspensions with the gadolinium content varied by changing number of Gd³⁺ ions grafted per each DND particle whereas the DND content in each suspension was kept the same. Such an approach to vary the contrast agent content differs from that commonly used in the relaxivity measurements. In the common approach, contrast agents are directly dissolved/suspended in media. Aiming to test validity of the unconventional approach, in the present study we follow the common way of measurement relaxivity: using variable concentrations of carriers (DND particles) in aqueous suspension keeping the number of Gd³⁺ ions per each carrier fixed. Materials and methods: ¹H NMR relaxation measurements of aqueous suspensions of DND with Gd³⁺ ions directly grafted to the DND surface were carried out at room temperature (293 K or 20 °C) in the external magnetic field B₀ = 8.0 T. Results and conclusions: Comparative study of two approaches for measuring relaxivity in suspensions containing DND as magnetic entities' carriers reveals complete identity of techniques in use.