Metal Ion/Tannic Acid Assembly as a Versatile Photothermal Platform in Engineering Multimodal Nanotheranostics for Advanced Applications

This study reports a family of photothermal materials, metal ion/tannic acid assemblies (MITAs). MITAs from Fe^III, V^III, and Ru^III afford excellent photothermal efficiency (η ≈ 40%). Sharply differing from the currently existing photothermal agents, MITAs are highlighted by merits including green synthesis, facile incorporation of diagnostic metal ions, and particularly topology-independent adhesion. Owing to the adhesion nature of MITAs, various kinds of MITA-based nanoengineerings are readily available via the self-adhesion of MITAs onto diverse templates, enabling MITAs well suited as a photothermal platform for versatile combination with other therapy approaches and imaging techniques. As a proof of concept, polymeric/inorganic nanoparticle/nanovesicle-supported Fe^III-tannic acid (Fe^IIITA) is fabricated. The photothermal effect is shown to be unaffected by the template origin and type and Fe^IIITA thickness on the templates. We validate the potency of nanovesicle-supported Fe^IIITA (PNV@Fe^IIITA) for tumor-specific photoactivated utilizations, including NIR photothermal therapy with complete tumor elimination, photothermal imaging (PTI), and photoacoustic imaging (PAI) in addition to T₁-MRI imaging. PNV@Fe^IIITA can be simultaneously equipped with functionalities, including T₂-MRI imaging by additionally doping Mn^II and NIR fluorescence imaging by encapsulating a hydrophilic NIR fluoroprobe. MITA demonstrates unparalleled superiority as a photothermal platform in engineering multimodal theranostics for advanced applications.