Influence of magnetoplasmonic γ-Fe 2 O 3 /Au core/shell nanoparticles on low-field nuclear magnetic resonance.

Magnetoplasmonic nanoparticles, composed of a plasmonic layer and a magnetic core, have been widely shown as promising contrast agents for magnetic resonance imaging (MRI) applications. However, their application in low-field nuclear magnetic resonance (LFNMR) research remains scarce. Here we synthesised γ-Fe2 O3 /Au core/shell (γ-Fe2 O3 @Au) nanoparticles and subsequently used them in a homemade, high-Tc , superconducting quantum interference device (SQUID) LFNMR system. Remarkably, we found that both the proton spin-lattice relaxation time (T1 ) and proton spin-spin relaxation time (T2 ) were influenced by the presence of γ-Fe2 O3 @Au nanoparticles. Unlike the spin-spin relaxation rate (1/T2 ), the spin-lattice relaxation rate (1/T1 ) was found to be further enhanced upon exposing the γ-Fe2 O3 @Au nanoparticles to 532 nm light during NMR measurements. We showed that the photothermal effect of the plasmonic gold layer after absorbing light energy was responsible for the observed change in T1 . This result reveals a promising method to actively control the contrast of T1 and T2 in low-field (LF) MRI applications.