Manganese‐Dioxide‐Coating‐Instructed Plasmonic Modulation of Gold Nanorods for Activatable Duplex‐Imaging‐Guided NIR‐II Photothermal‐Chemodynamic Therapy

Abstract

and background absorption than that done in the first near-infrared window (NIR-I, 650-950 nm). [1] Therefore, the development of theranostic agents in NIR-II region has become something of a research hotspot. [1a,2] Recently, there is an ever-increasing number of papers describing the modification of gold nanomaterials for NIR-II photoacoustic imaging (PAI) and photothermal therapy (PTT) owing to its unique plasmonic, acoustic, and electric properties, as well as multifunctionality endowed by its various dimensions and morphologies. [1c,e,3] Furthermore, its excellent biosafety surpasses the limits of most inorganic nanomaterials. [4] Currently, there are few methods that shift the localized surface plasmon resonance (LSPR) peak of gold nanomaterials from NIR-I to NIR-II region. [2a,5] For instance, some gold nanorods (GNRs) with superhigh aspect ratios or GNRs with extremely thin shells have been reported. [6] However, most of them still bear poor photostability. In fact, tailoring the morphology is not the only method to obtain a redshift in the absorbance of gold nanomaterials. Substances coated to the surface of GNRs can also cause absorbance red or blueshifts. For example, Wu et al. found that a layer of Cu 2 O could cause absorbance redshift of GNRs from 600 to 800 nm. [7] Yeh et al. developed a rattle-like structure with a GNR encapsulated in a cavity of AuAg nanoshell to achieve a broad absorbance band span 300-1350 nm. [2a] However, most metal oxides suffer from biotoxicity and not responsive to tumor microenvironment. Therefore, the development of biocompatible and stimuli-responsive coatings for plasmonic modulation of GNRs remains a big challenge. Manganese is one of the most commonly used metal element in cancer theranostics on account of its good biosafety and rich quantity of valence states, which allows for the design and synthesis of intelligent theranostic agents. [8] For example, manganese dioxide (MnO 2) is widely used as a catalase to decompose hydrogen peroxide (H 2 O 2) in tumor microenvironment and produce oxygen and hence relieves the tumor hypoxia and reduces tumor resistance to radio-or chemotherapy. [9] Recently, it was reported that MnO 2 could decrease glutathione level in Nanotheranostic agents of gold nanomaterials in the second near-infrared (NIR-II) window have attracted significant attention in cancer management, owing to the reduced background signal and deeper penetration depth in tissues. However, it is still challenging to modulate the localized surface plasmon resonance (LSPR) of gold nanomaterials from the first near-infrared (NIR-I) to NIR-II region. Herein, a plasmonic modulation strategy of gold nanorods (GNRs) through manganese dioxide coating is developed for NIR-II photoacoustic/magnetic resonance (MR) duplex-imaging-guided NIR-II photothermal chemodynamic therapy. GNRs are coated with silica dioxide (SiO 2) and then covered with magnesium dioxide (MnO 2) to obtain the final product of GNR@SiO 2 @MnO 2 (denoted as GSM). The LSPR peak of GNRs could be tuned by adjust...

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