Biocompatible fluorophores for shortwave infrared imaging

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Optical imaging is a safe, cost-effective, rapid imaging modality, which can be multiplexed or engineered to have a turn-on response. Despite these advantages, optical imaging is not widely employed in the clinic due to the poor penetration of light through tissue and high background signal from endogenous chromophores. The shortwave infrared (SWIR) region of the electromagnetic spectrum has emerged as an optimal region for optical imaging due to the decreased scattering of light by tissue and minimal autofluorescence of endogenous biomolecules in this region. The potential of the SWIR has been showcased using carbon nanotubes and quantum dots as contrast agents; however, toxicity concerns regarding these materials prevent their clinical translation. What is necessary are bright, non-toxic shortwave infrared fluorophores. Recently, we have reported a bright polymethine fluorophore, deemed Flav7, which absorbs and emits shortwave infrared light. We will take this exciting first generation compound and transform Flav7 into a water- soluble contrast agent that can be appended to targeting agents and biomolecules of interest. We will improve nanomaterial formulations of Flav7 by synthesizing fluorous-soluble variants. Simultaneously, we will modify the chromophore structure to enhance the photophysical properties and access fluorophores that can be employed simultaneously for multiplexed SWIR imaging. Lastly, we will develop SWIR quenchers, which will be linked to the fluorophores using protease-cleavable peptide sequences to access SWIR responsive probes. Responsive probes offer enhanced signal-to-noise ratios and eliminate the need to wait for fluorophores to clear. Visible and near-infrared versions of similar responsive probes are currently in clinical trials for image- guided surgery. Collectively, our fluorophore development work will provide the foundation for intraoperative imaging, fluorescent endoscope-based diagnostics, and optical mammography.