Organic NIR-II Nanofluorophore with Ultrahigh Quantum Yield for Vessels Imaging and Fluorescence Image-Guided Surgery

The second near-infrared window (NIR-II) fluorescence imaging has aroused more and more interest in biomedical applications due to negligible autofluorescence and deep penetration ability. However, the fluorescence quantum yield of NIR-II fluorophores with more than 1100 nm emission wavelength is typically less than 1%, thus limiting the imaging quality of deep tissues. In this study, a novel NIR-II organic small molecule CTB1125 is designed and synthesized. Due to an efficient intramolecular charge transfer (ICT) facilitated by a high donor-acceptor-donor (D-A-D) strength structure, CTB1125 exhibits a maximum emission wavelength of 1125 nm. Additionally, branched alkyl chains are modified on the conjugated fused ring backbone to reduce intermolecular stacking. CTB1125 is encapsulated in the amphiphilic copolymer PS2000-PEG2000 to form CTB1125-NPs, which exhibit ultrahigh fluorescence quantum yield up to 4.84% in aqueous solution, excellent photostability, and high signal-to-noise rate. Due to these outstanding properties, CTB1125-NPs have been successfully used for clear and long-duration NIR-II vessel imaging with small amounts of CTB1125-NPs, low laser power and short exposure time, and precisely guiding the surgical resection of tumors in mice through fluorescence imaging. This work provides a promising NIR-II fluorophore with ultrahigh brightness for deep-tissue imaging and imaging-guided surgery.