Redox-Induced Ostwald Ripening of Ultrasmall Gold Nanoparticles for H₂O₂‑Activated Photoacoustic Imaging

Microenvironment-responsive imaging has tremendous application potential in disease diagnosis. Elevated levels of hydrogen peroxide (H₂O₂) have been observed in tumor and inflammation tissues, making it an ideal endogenous molecule for microenvironment-activated diagnostics. In this study, we prepared an activatable plasmonic theranostics system based on silica-carried ultrasmall gold nanoparticles (SiO₂@usAu NPs). The SiO₂@usAu NPs underwent an Ostwald ripening process in response to the overexpressed H₂O₂ in the microenvironment. A red shift in the ultraviolet–visible light (UV-vis) absorption spectrum was observed after the Ostwald redox reaction, transitioning from the UV-vis to near-infrared (IR) region, accompanied by an augmentation in the size of the gold nanoparticles. With the H₂O₂-activated characteristics, SiO₂@usAu NPs are considered to be a suitable responsive photoacoustic imaging contrast agent. Furthermore, in vivo experiments demonstrate that the SiO₂@usAu NPs showed good in vivo photoacoustic imaging performance both in the 4T1 tumor model and the LPS-induced peritonitis model, suggesting that it could be used as a responsive photoacoustic imaging contrast agent for noninvasive detection and diagnosis of diseases in vivo, including cancers and inflammation-related diseases with exceptional sensitivity and precision. The remarkable microenvironment-responsive characteristics of SiO₂@usAu NPs offer novel prospects for the advancement of light-regulated nanoplatforms for noninvasive and accurate diagnosis.