Abstract
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-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-Fe2O3@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-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 T1. This result reveals a promising method to actively control the contrast of T1 and T2 in low-field (LF) MRI applications.
Highlights
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
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
It is well known that magnetic resonance imaging (MRI) is a powerful, non-invasive technique that has been widely applied to the clinical diagnosis of diseases
Summary
The average hydrodynamic size (i.e. diameter) of the synthesised γ-Fe2O3@Au nanoparticles, determined by dynamic light scattering (DLS) (Nanotrac-150, Microtrac), was 28.38 ± 6.26 nm. Here we ensured constant sample temperature using very-low-power laser irradiation (100 μW) during the experiment, it seems that this energy is still high enough to influence the motion of magnetic γ-Fe2O3@Au nanoparticles. The enhanced correlation and the increased diffusion correlation time both facilitate the proton spins to effectively release their rf pulse magnetic energy back to the surrounding and shorten T1 after light irradiation. The correlation between water protons and MNPs cannot be effectively enhanced by light irradiation, and the T1 relaxation time remained unchanged. The core–shell γ-Fe2O3@Au nanoparticles can effectively enhance the 1/T1 relaxation rate under light irradiation These results strongly support our assumptions and prove that the unique core–shell structure of the γ-Fe2O3@Au nanoparticles allows control of T1 by light irradiation within the LFNMR system
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