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.
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