Shortwave infrared fluorescence imaging of peripheral organs in awake and freely moving mice

Palladium-Catalyzed Functionalization of Shortwave Infrared Heptamethine Fluorophores Expands Their In Vivo Utility

Fluorescence imaging in the near-infrared (NIR, 700-1000 nm) and shortwave infrared (SWIR, 1000-2000 nm) regions is advantageous for studying mammals. This work applies palladium-catalyzed coupling methods to functionalize flavylium and chromenylium SWIR polymethine fluorophores, which are challenging substrates due to their small HOMO-LUMO gaps. These chemistries include Suzuki-Miyaura and Sonogashira couplings as well as an unprecedented coupling of alcohol substrates to ultimately achieve a panel of C-CAr, C-Csp, and C-O-alkyl functionalized SWIR fluorescent heptamethine dyes. The photophysical properties of the resulting fluorophores are analyzed against Hammett parameters to produce predictive metrics for absorption maxima. These metrics are strategically applied in the design of laser-matched, SWIR-emissive, chromenylium heptamethine dyes. Added functionalities advance the utility of SWIR fluorophores by increasing brightness in micelle formulations, modulating lipophilicity for alternative delivery vehicles, and enabling bioconjugation to targeting moieties. Ultimately, three functionalized fluorophores are employed in concert to achieve multicolor excitation-multiplexed imaging in murine cancer models.

High-Resolution Multicolor Shortwave Infrared Dynamic In Vivo Imaging with Chromenylium Nonamethine Dyes

Imaging in the shortwave infrared (SWIR) region offers fast, high-resolution visualization of in vivo targets in a multiplexed manner. These methods require bright, bathochromically shifted fluorescent dyes with sufficient emission at SWIR wavelengths-ideally above 1500 nm for high-resolution deep tissue imaging. Polymethine dyes are a privileged class of contrast agents due to their excellent absorption and high degree of modularity. In this work, we push flavylium and chromenylium dyes further into the SWIR region through polymethine chain extension. This panel of nonamethine dyes boasts absorbances as red as 1149 nm and tail emission beyond 1500 nm. These dyes are the brightest organic fluorophores at their respective bandgaps to date, with εmax ∼ 105 M-1 cm-1 and ΦF up to 0.5%. Using two nonamethine dyes, Chrom9 and JuloFlav9, we performed two-color all-SWIR multiplexed imaging (Excitation at 1060 and 1150 nm; Emission collection at >1500 nm), enhancing the depths and resolutions able to be obtained in multicolor SWIR imaging with small molecule contrast agents. Finally, we combine the nonamenthine dyes with other SWIR-emissive fluorophores and demonstrate five-color awake imaging in an unrestrained mouse, simultaneously pushing the multiplexing, resolution, and speed limits of in vivo optical imaging.