High‐Aspect‐Ratio Plasmonic Heterostructures for In Vivo Enhanced Optical Coherence Tomography Imaging in the Second Near‐Infrared Biological Window

Abstract Optical coherence tomography (OCT) is a noninvasive bio‐imaging modality that is widely used in both fundamental research and clinical practice. Contrast agents with strong light‐scattering properties are a prerequisite for OCT imaging. Bio‐imaging in the second near‐infrared window (NIR‐II, 1000–1700 nm) has recently attracted significant attention based on reduced light absorption, suppressed photon scattering, and negligible autofluorescence. OCT contrast agents with both strong light‐scattering cross‐sections in the NIR‐II window and excellent biocompatibility are highly desirable. In this article, Ag‐based rod‐shaped plasmonic nanostructures are presented as NIR‐II OCT contrast agents. As a high‐aspect‐ratio heterostructure, the Ag nanorods coated with mesoporous silica shells (AgNR@mSiO₂) are developed to achieve plasmon resonance at 1330 nm and excellent biocompatibility. By taking advantage of their huge light‐scattering cross‐sections, which provide the strongest scattering reported to date among various nanoscale OCT contrast agents, the heterostructures are used to perform efficient in vivo OCT imaging of crucian carp eyes and chicken blood vessels in the NIR‐II window. The captured images exhibit enhanced contrast with large imaging depth. These results demonstrate that the developed AgNR@mSiO₂ heterostructures are promising OCT contrast agents, that can provide guidance and reference for the development of highly efficient NIR‐II imaging probes.