This study aims to design and evaluate a two-dimensional Ti 3 C 2 -MXene contrast agent, codoped with iron and manganese, with the aim of achieving T 1 /T 2 dual-mode magnetic resonance imaging contrast, and to investigate its effect on Chemical Exchange Saturation Transfer (CEST) contrast agents. Single-layer Ti 3 C 2 was synthesized via the HCL/LiF etching technique, with the flake size subsequently tailored and the hydroxylated surface modified through a hydrothermal process. Fe 3 O 4 nanoparticles and MnO 2 nanosheets were integrated onto the two-dimensional Ti 3 C 2 -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 B 1 = 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.
The development of T 1 -T 2 dual-mode contrast agents is expected to improve cancer diagnostic capabilities in response to the limitation of traditional single-mode magnetic resonance imaging (MRI) contrast agents. In this study, a pH-responsive dual-mode MRI nanoprobe, Fe 3 O 4 @MnS-transferrin (FMT), is prepared with the objective of augmenting tumor visualization and chemodynamic therapy (CDT). FMT achieved precise tumor targeting by binding to transferrin receptors on cancer cells via the transferrin molecules on their surface. FMT underwent pH-responsive decomposition in the acidic tumor microenvironment, releasing Fe 3 O 4 and Mn 2+ . This decomposition increased the spatial separation between Fe 3 O 4 and Mn 2+ , attenuating the mutual magnetic shielding effect and activating dual-mode MRI function. Moreover, FMT released Mn 2+ and hydrogen sulfide (H 2 S). Mn 2+ triggered a Fenton-like reaction, generating reactive oxygen species that induced cytotoxicity through CDT. Concurrently, H 2 S inhibited catalase activity, providing additional substrates for the Fenton-like reaction, thereby amplifying CDT in a cascading manner. This synergistic mechanism amplified the cytotoxicity of CDT, enhancing the efficacy of tumor treatment and metastasis inhibition. Therefore, FMT demonstrated significant promise for enhancing both the precision of tumor imaging and the efficacy of treatment.
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