Bimodal Phosphorescence–Magnetic Resonance Imaging Nanoprobes for Glutathione Based on MnO₂ Nanosheet–Ru(II) Complex Nanoarchitecture

Bimodal fluorescence–magnetic resonance imaging (MRI) technique has shown great utilities in bioassays because it combines the advantages of both optical imaging and MRI to provide more sufficient information over any modality alone. In this work, on the basis of a MnO2 nanosheet–Ru(II) complex nanoarchitecture, a bimodal phosphorescence–MRI nanoprobe for glutathione (GSH) has been constructed. The nanoprobe, Ru(BPY)3@MnO2, was constructed by integrating MnO2 nanosheets with a phosphorescent Ru(II) complex [Ru(BPY)3](PF6)2 (BPY = 2,2′-bipyridine), which resulted in complete phosphorescence quenching of the Ru(II) complex, accompanied by very low longitudinal and transverse relaxivity. Upon exposure to GSH, the reduction of MnO2 nanosheets by GSH triggers a recovery of phosphorescence and simultaneously produces a number of Mn2+ ions, a perfect MRI contrast agent. The as-prepared nanoprobe showed good water dispersion and biocompatibility and a rapid, selective, and sensitive response toward GSH in the phosphorescence and MR detection modes. The practicability of the nanoprobe was proved by time-gated luminescence assay of GSH in human serum, phosphorescent imaging of endogenous GSH in living cells, zebrafish, and tumor-bearing mice, as well as the MRI of GSH in tumor-bearing mice. The research outcomes suggested the potential of Ru(BPY)3@MnO2 for the bimodal phosphorescence–MRI sensing of GSH in vitro and in vivo.