Chromenylium\nStar Polymers: Merging Water Solubility\nand Stealth Properties with Shortwave Infrared Emissive Fluorophores

Fluorescence imaging in the shortwave infrared (SWIR)\nregion has\nemerged as a vital tool for studying mammals. SWIR emissive polymethine\ndyes are well-suited to this endeavor; however, advancing <i>in vivo</i> imaging utility with these dyes is primarily limited\nby hydrophobicity and/or nonspecific protein association. Herein,\nwe take a distinct approach to combine hydrophilicity and stealth\nbehavior to construct bright, SWIR emissive chromenylium fluorophores\nby employing a well-defined poly(2-methyl-2-oxazoline) (POx) star\npolymer architecture, which we refer to as chromenylium stars, or\n“CStars.” Of these polymer-shielded dyes, the variant\ncontaining five POx chains (<b>CStar30</b>) boasts particularly\nenhanced aqueous solubility and SWIR brightness, enabling high-resolution\nSWIR imaging in mice. The swift renal clearance and stealth behavior\ndisplayed <i>in vivo</i> also achieves improved noninvasive\nvisualization of the lymphatic system. Further, CStar’s orthogonal\nbiodistribution to an FDA-approved dye, indocyanine green (<b>ICG</b>), facilitates excitation-multiplexed SWIR imaging in two colors\nto achieve simultaneous visualization of both fluid dynamics and protein\ndynamics in the same animal in real time at video-rate frame counts.