Near-Infrared II Semiconducting Polymer Dots: Chain Packing Modulation and High-Contrast Vascular Imaging in Deep Tissues

Fluorescence imaging in the secondnear-infrared (NIR-II) windowhas attracted considerable interest in investigations of vascularstructure and angiogenesis, providing valuable information for theprecise diagnosis of early stage diseases. However, it remains challengingto image small blood vessels in deep tissues because of the strongphoton scattering and low fluorescence brightness of the fluorophores.Here, we describe our combined efforts in both fluorescent probe designand image algorithm development for high-contrast vascular imagingin deep turbid tissues such as mouse and rat brains with intact skull.First, we use a polymer blending strategy to modulate the chain packingbehavior of the large, rigid, NIR-II semiconducting polymers to producecompact and bright polymer dots (Pdots), a prerequisite for in vivo fluorescence imaging of small blood vessels. Wefurther developed a robust Hessian matrix method to enhance the imagecontrast of vascular structures, particularly the small and weaklyfluorescent vessels. The enhanced vascular images obtained in whole-bodymouse imaging exhibit more than an order of magnitude improvementin the signal-to-background ratio (SBR) as compared to the originalimages. Taking advantage of the bright Pdots and Hessian matrix method,we finally performed through-skull NIR-II fluorescence imaging andobtained a high-contrast cerebral vasculature in both mouse and ratmodels bearing brain tumors. This study in Pdot probe developmentand imaging algorithm enhancement provides a promising approach forNIR-II fluorescence vascular imaging of deep turbid tissues.

Automated summary

Researchers have developed a method for high-contrast vascular imaging in deep tissues using fluorescent probes and imaging algorithms. By improving the brightness and compactness of the probes, and enhancing the image contrast using the Hessian matrix method, they achieved high-resolution imaging of small blood vessels. This study provides a promising approach for NIR-II fluorescence imaging of vascular structures in deep tissues.