Experimental study on transverse relaxation rate of protons in aqueous suspensions of magnetite nanocrystal clusters with a SiO2 shell

The transverse relaxation rate (1/T2) of aqueous suspensions of magnetite nanocrystal clusters with a SiO2 shell of different thicknesses has been studied experimentally. With the increase of the shell thickness, 1/T2 decreases slightly due to the aggregation of clusters during coating process. In T2 measurement, the waiting time dependence decreases when the shell gets thicker, because of the decreased magnetic attractive energy, particle number concentration and diffusion coefficient of magnetite nanocrystal clusters with a thicker SiO2 shell. These experimental results, supporting the relaxation theory and computer simulations, may promote future development of magnetic contrast agents.