Preparation of Fe–Mn Codoped 2D MXene Nanoprobes and Feasibility Study of Combining With CEST for Multimodal Imaging

This study aims to design and evaluate a two-dimensional Ti₃C₂-MXene contrast agent, codoped with iron and manganese, with the aim of achieving T₁/T₂ dual-mode magnetic resonance imaging contrast, and to investigate its effect on Chemical Exchange Saturation Transfer (CEST) contrast agents. Single-layer Ti₃C₂ was synthesized via the HCL/LiF etching technique, with the flake size subsequently tailored and the hydroxylated surface modified through a hydrothermal process. Fe₃O₄ nanoparticles and MnO₂ nanosheets were integrated onto the two-dimensional Ti₃C₂-MXene surface using an in situ doping approach, and the final modification was achieved with carboxymethyl chitosan. Various characterization techniques were employed to assess the physical and chemical properties of the probe, which were then combined with a CEST contrast agent to investigate the mechanisms of multimodal magnetic resonance imaging and in vitro photothermal effects. Upon integrating the multi-modal molecular probe with Ioversol for imaging purposes, at a magnetic field strength of B₁ = 1.25 μT and with a molecular probe concentration of 0.5 mg/mL, the CEST signal from Ioversol is almost entirely suppressed. This allows for the successful identification of a distinct concentration range where both contrast agents can coexist. In vitro photothermal studies on MXene codoped with iron and manganese have shown that the composite molecular probe exhibits excellent photothermal efficiency. The method combining complex nanoprobes with CEST contrast agents successfully achieved simultaneous imaging of both contrast agents. In vitro MRI experiments successfully obtained distinguishable concentration ranges for both, with changes in CEST signals reflecting the concentration variations of the complex molecular probes, which also exhibit good photothermal therapy (PTT) capabilities.