Near-Infrared Fluorescent Nanoparticles from Reactive Polymers for Bioimaging

The sensitivity of biological imaging can be significantly enhanced by near-infrared (NIR) fluorescent dyes, which offer deep tissue penetration and low background interference. However, their practical application in targeted imaging is limited by low fluorescence intensity at the sites of interest, primarily caused by restricted availability of cellular binding sites and the hydrophobic nature of most NIR dyes, leading to compromised solubility and stability in aqueous milieus. To address these challenges, we design and synthesize a series of functional fluorescent polymers using poly(pentafluorophenyl acrylate) (PPFPA) as a versatile precursor for targeted modifications. The synthesis involves the conjugation of amine-functionalized IR775 NIR dye to the reactive PFP ester units, followed by the incorporation of poly(ethylene glycol) (PEG) chains to enhance hydrophilicity and biocompatibility. By tuning the dye-to-PEG ratio, the fluorescence intensity and self-assembly behavior of the polymers are modulated, yielding spherical nanoparticles with enhanced brightness at a dye loading of 25%. Biotinylation of the fluorescent copolymers then enables their targeted binding to biotin-receptor-containing surfaces. Enhancement in fluorescence signal detection postcellular internalization is demonstrated by in vitro imaging, and an increase in tissue penetration depth is shown by employing a tissue-like phantom model, validating the use of the developed fluorescent polymers as NIR probes for advanced imaging and diagnostic applications.