Developing a feasible way to feature longitudinal (T1) and transverse (T2) relaxation performance of
contrast agents for magnetic resonance imaging (MRI) is important in
cancer diagnosis and
therapy. Improved accessibility to water molecule is essential for accelerating the relaxation rate of water
protons around the
contrast agents. Ferrocenyl compounds have reversible redox property for modulating the hydrophobicity/hydrophilicity of assemblies. Thus, they could be the candidates that can change water accessibility to the
contrast agent surface. Herein, we incorporated ferrocenylseleno compound (FcSe) with Gd3+-based paramagnetic UCNPs, to obtain FNPs-Gd nanocomposites using T1-T2 MR/UCL trimodal imaging and simultaneous photo-Fenton
therapy. When the surface of
NaGdF4:Yb,Tm UNCPs was ligated by FcSe, the hydrogen bonding between hydrophilic
selenium and surrounding water molecules accelerated their
proton exchange to initially endow FNPs-Gd with high r1 relaxivity. Then,
hydrogen nuclei from FcSe disrupted the homogeneity of the magnetic field around the water molecules. This facilitated T2 relaxation and resulted in enhanced r2 relaxivity. Notably, upon the near-infrared light-promoted Fenton-like reaction in the tumor microenvironment, hydrophobic
ferrocene(II) of FcSe was oxidized into hydrophilic
ferrocenium(III), which further increased the relaxation rate of water
protons to obtain r1 = 1.90±0.12 mM-1 s-1 and r2 = 12.80±0.60 mM-1 s-1. With an ideal relaxivity ratio (r2/r1) of 6.74, FNPs-Gd exhibited high contrast potential of T1-T2 dual-mode MRI in vitro and in vivo. This work confirms that
ferrocene and
selenium are effective boosters that enhance the T1-T2 relaxivities of MRI
contrast agents, which could provide a new strategy for multimodal imaging-guided photo-Fenton
therapy of
tumors. STATEMENT OF SIGNIFICANCE: T1-T2 dual-mode MRI nanoplatform with tumor-microenvironment-responsive features has been an attractive prospect. Herein, we designed redox ferrocenylseleno compound (FcSe) modified paramagnetic Gd3+-based UCNPs, to modulate T1-T2 relaxation time for multimodal imaging and H2O2-responsive photo-Fenton
therapy.
Selenium-hydrogen bond of FcSe with surrounding water molecules facilitated water accessibility for fast T1 relaxation.
Hydrogen nucleus in FcSe perturbed the phase coherence of water molecules in an inhomogeneous magnetic field and thus accelerated T2 relaxation. In tumor microenvironment, FcSe was oxidized into hydrophilic
ferrocenium via NIR light-promoted Fenton-like reaction which further increased both T1 and T2 relaxation rates; Meanwhile, the released toxic •OH performed on-demand
cancer therapy. This work confirms that FcSe is an effective redox mediate for multimodal imaging-guided
cancer therapy.