Activatable NIR‐II Plasmonic Nanotheranostics for Efficient Photoacoustic Imaging and Photothermal Cancer Therapy

Abstract Precise manipulation of optical properties through the structure‐evolution of plasmonic nanoparticles is of great interest in biomedical fields including bioimaging and phototherapy. However, previous success has been limited to fixed assembled structures or visible–NIR‐I absorption. Here, an activatable NIR‐II plasmonic theranostics system based on silica‐encapsulated self‐assembled gold nanochains (AuNCs@SiO 2 ) for accurate tumor diagnosis and effective treatment is reported. This transformable chain structure breaks through the traditional molecular imaging window, whose absorption can be redshifted from the visible to the NIR‐II region owing to the fusion between adjacent gold nanoparticles in the restricted local space of AuNCs@SiO 2 triggered by the high H 2 O 2 level in the tumor microenvironment (TME), leading to the generation of a new string‐like structure with strong NIR‐II absorption, which is further confirmed by finite‐difference‐time‐domain (FDTD) simulation. With the TME‐activated characteristics, AuNCs@SiO 2 exhibits excellent properties for photoacoustic imaging and a high photothermal conversion efficiency of 82.2% at 1064 nm leading to severe cell death and remarkable tumor growth inhibition in vivo. These prominent intelligent TME‐responsive features of AuNCs@SiO 2 may open up a new avenue to explore optical regulated nano‐platform for intelligent, accurate, and noninvasive theranostics in NIR‐II window.