Influence of magnetoplasmonic γ-Fe₂O₃/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-Fe₂O₃/Au core/shell (γ-Fe₂O₃ @Au) nanoparticles and subsequently used them in a homemade, high-T c, superconducting quantum interference device (SQUID) LFNMR system. Remarkably, we found that both the proton spin-lattice relaxation time (T ₁) and proton spin-spin relaxation time (T₂) were influenced by the presence of γ-Fe₂O₃ @Au nanoparticles. Unlike the spin-spin relaxation rate (1/T₂), the spin-lattice relaxation rate (1/T ₁) was found to be further enhanced upon exposing the γ-Fe₂O₃ @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 T ₁. This result reveals a promising method to actively control the contrast of T ₁ and T₂ in low-field (LF) MRI applications.