Study of γ-Fe₂O₃/Au core/shell nanoparticles as the contrast agent for high-T_c SQUID-based low field nuclear magnetic resonance

To improve the image contrast, the so-called contrast agents (CAs) are often used in magnetic resonance image (MRI). CAs are generally paramagnetic or superparamagnetic nanoparticle suspensions. To increase the applicability of low field nuclear magnetic resonance (LFNMR) or LFMRI system, CAs also have been introduced to enhance the image contrast. In this work, we synthesized the γ-Fe₂O₃/Au core/shell (γ-Fe₂O₃@Au) nanoparticle and applied it to a homemade high-T_c SQUID-based LFNMR system to study the characteristics of γ-Fe₂O₃@Au nanoparticle as the contrast agent for the LFNMR system. The average hydrodynamic sizes of the synthesized γ-Fe₂O₃@Au nanoparticles are 28.38 ± 6.26 nm in diameter. The γ-Fe₂O₃@Au nanoparticles exhibit a characteristic absorption peak at 536 nm from the contribution of localized surface plasmon resonance of Au shell. The spin-lattice relaxation rate, 1/T₁, and the spin-spin relaxation rate, 1/T₂, varied with the concentration of γ-Fe₂O₃@Au nanoparticle. Compared with the data measured in high field (7 Tesla), we found that the γ-Fe₂O₃@Au nanoparticle is a promising T₁-relaxing CA for LFNMR.