Advanced optical materials: near infrared two region optical coherence tomography based on high aspect ratio plasmon nanostructures

In recent years near-infrared light with high penetration depth of biological tissue has been widely used in various biological imaging. Compared with visible light (450-650 nm) nir-i (650-950 nm nir-ii) nir-ii (950-1700 nm nir-ii) has less absorption scattering in biological tissues the background fluorescence of biological tissues is weaker. This makes the biological imaging technology based on nir-ii region attracted much attention. Compared with other imaging technologies optical coherence tomography (OCT) has the advantages of non-destructive large imaging depth high imaging resolution which is widely used in clinical diagnosis research. However due to the small refractive index difference of biological tissue the contrast of OCT imaging quality is low which limits its imaging sensitivity. An effective way to improve the imaging quality of OCT is to add exogenous contrast agent with high light scattering cross section. Surface plasmon (SP) metal nanostructures exhibit extremely high light scattering cross sections when they are excited at resonance which makes them become a highly concerned OCT contrast agent in nir-ii region. At present gold nanostructures (such as gold nanorods gold nanoshell gold triangle plate gold nanoring gold nanoconical) are the main SP nanostructures used in nir-ii OCT contrast agents. Compared with gold nanostructures of the same size silver nanostructures have narrower SP resonance peak width higher light scattering cross section which make them have greater advantages as OCT imaging contrast agents. However it is difficult for the existing silver nanostructures to adjust their SP resonance to the nir-ii region. On the other h the cytotoxicity instability of silver nanostructures restrict their application in biomedical field.

to solve the above problems the research team of Professor Deng Shaozhi from school of electronic information engineering Sun Yat sen University China prepared a kind of SP silver nano heterostructure with high aspect ratio (> 8) by two-step wet chemical growth method（ AgNR@mSiO2 ）。 The heterostructure is a core-shell structure: silver nanorods epitaxially grown on gold nanocones are used as the core mesoporous silica coating is used as the shell. Due to its high aspect ratio the SP resonance peak of the heterostructure is located at 1330 nm exhibits a large light scattering cross section (3.7 × 105 Nm2) which is the maximum value of the reported OCT nano contrast agent. At the same time the existence of mesoporous silica shell insulates the silver nanorods from the external environment which makes the heterostructures show excellent biocompatibility stability. On this basis the research team cooperated with Professor Zhou Jianhua's research group of School of Biomedical Engineering Sun Yat sen University to AgNR@mSiO2 Nano heterostructures are used as contrast agents in Oct enhancement imaging. The experimental results of in vitro model imaging show that under the illumination of imaging laser with central wavelength of 1310 nm AgNR@mSiO2 Nano heterostructure can significantly improve the imaging contrast depth of Oct. Furthermore due to the excellent biocompatibility of the heterostructure fish eye chicken arterial blood vessels were used as animal models in vivo high-quality OCT imaging of nir-ii region was also obtained The researchers believe that this study demonstrates the advantages of silver based SP nanostructures as a contrast agent for OCT imaging in nir-ii region thus providing a new idea for the development of high-quality imaging contrast agent for nir-ii region based on scattering imaging.

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