Synthesis and characterization of Fe- and Co-based ferrite nanoparticles and study of the T_ 1 and T_ 2 relaxivity of chitosan-coated particles

摘要

In pursuit of newer and more effective contrast agents for magnetic resonance imaging, we report in this article the use of biocompatible chitosan-coated ferrite nanoparticles of different kinds with a view to determine their potential applications as the contrast agents in the field of nuclear magnetic resonance. The single-phase ferrite particles were synthesized by chemical co-precipitation (CoFe_2O_4 and Fe_ 3O_4) and by applying ultrasonic vibration (CoFe_ 2O_4 and Co_(0.8)Zn_(0.2)Fe_ 2O_4). Although magnetic anisotropy of CoFe_ 2O_4 nanoparticle leads to finite coercivity even for nanoensembles, it has been reduced significantly to a minimum level by applying ultrasonic vibration. Fe_3O_4 synthesized by chemical co-precipitation yielded particles which already possess negligible coercivity and remanence. Substitution of Co by Zn in CoFe_2O_4 increases the magnetization significantly with a small increase in coercivity and remanence. Particles synthesized by the application of ultrasonic vibration leads to the higher values of T_ 2 relaxivities than by chemical coprecipitation. We report that the T_ 2 relaxivities of these particles are of two orders of magnitude higher than corresponding T_ 1 relaxivities. Thus, these particles are evidently suitable as contrast agent for T_ 2 weighted MR images.