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 III TA) is fabricated. The photothermal effect is shown to be unaffected by the template origin and type and Fe III TA thickness on the templates. We validate the potency of nanovesicle-supported Fe III TA (PNV@Fe III TA) for tumor-specific photoactivated utilizations, including NIR photothermal therapy with complete tumor elimination, photothermal imaging (PTI), and photoacoustic imaging (PAI) in addition to T 1 -MRI imaging. PNV@Fe III TA can be simultaneously equipped with functionalities, including T 2 -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.