Redox chemistry-enabled stepwise surface dual nanoparticle engineering of 2D MXenes for tumor-sensitive T 1 and T 2 MRI-guided photonic breast-cancer hyperthermia in the NIR-II biowindow.

With the fast advent of two-dimensional (2D) MXenes, several therapeutic paradigms based on 2D MXenes flourish, but a generic strategy for MXene functionalization to achieve theranostic functionalities and desirable performance is still lacking. In this work, we report a facile and efficient stepwise surface-functionalization strategy to achieve distinct tumor microenvironment (TME)-responsive T 1 and T 2 magnetic resonance (MR) imaging-guided photothermal breast-cancer hyperthermia in the second near-infrared (NIR-II) biowindow. This approach is based on the stepwise growth of superparamagnetic Fe 3 O 4 and paramagnetic MnO x nanocomponents onto the large surface of ultrathin 2D niobium carbide (Nb 2 C) MXene nanosheets (Fe 3 O 4 /MnO x -Nb 2 C) by making full use of the redox status/chemistry of the 2D MXene surface. Such a surface-nanoparticle engineering strategy endows Fe 3 O 4 /MnO x -Nb 2 C composite nanosheets with a series of properties that include high photothermal-conversion efficiency in the NIR-II biowindow (1064 nm, η 30.9%) for effective photothermal tumor eradication without further reoccurrence. It also allows TME-responsive T 1 - and T 2 -weighted MR imaging and high biocompatibility for guaranteeing further potential clinical transformation. This work not only makes the efficient diagnostic T 1 - and T 2 -weighted MR imaging-guided photonic hyperthermia of breast cancer possible, but also broadens the biomedical applications of MXene-based nanoplatforms by developing novel surface-engineering strategies to construct 2D Nb 2 C MXene-based composite multifunctional nanoplatforms.