[Polypyrrole Functionalized Gold Nanorods as Novel Contrast Agents for Optical Coherence Tomography]

Polypyrrole (PPy) is easy-prepared with good biocompatibility and strong absorption in near-infrared (NIR) region which can serve as both the photothermal therapeutic agent and contrast agent of optical coherence tomography (OCT) imaging. Herein, gold nanorod (GNR) modified with PPy (GNR-PPy) as contrast agent for optical coherence tomography imaging was investigated. GNR-PPy was synthesized via one-pot facile oxidative polymerization by using pyrrole and GNR as starting materials. Nanoparticles were characterized using ultraviolet-visible absorbance spectroscopy, Raman spectroscopy and transmission electron microscopy. A xenograft tumor mouse model was fabricated to study the OCT contrast effect of GNR-PPy on breast tumor. An OCT system equipped with an 840 nm SLED was used for OCT imaging of the tumors injected with gold nanostructures. The experimental results indicated that the penetration depth of the OCT signals from tumors injected with GNR-PPy was lower than that from tumors injected with gold nanorods, which could be ascribed to the stronger light activity of GNR-PPy in NIR region. To quantitatively analyze the contrast effect, the attenuation coefficients were extracted from the OCT images of tumors injected with the nanostructures. In comparison with the attenuation coefficient extracted from the OCT images containing GNR, the attenuation coefficient of tumors injected with GNR-PPy was significant higher. It was concluded that gold nanorods modified with polypyrrole can enhance the light absorption in near-infrared much better, which would provide a possible detection means for enhancing the contrast effect of tumor tissues.