Rational design of stable heptamethine cyanines and development of a biomarker-activatable probe for detecting acute lung/kidney injuries via NIR-II fluorescence imaging.

Developing high-quality dyes to construct activatable probes for analyte sensing via NIR-II fluorescence is critical for attaining enhanced imaging depths and resolution. Heptamethine cyanines can serve this purpose; however, they usually have poor stability and a tendency to self-aggregate. Herein, we present a design strategy involving the installation of pyridinium and tert-butyl groups onto the central cyclohexenyl core to increase steric crowding, enhance water solubility, and provide a site for the incorporation of analyte-responsive elements. The resulting NP-N dyes emit NIR-II light and can outperform benchmark heptamethine cyanines such as ICG. Using HP-N1, we developed HP-H2O2 and showed that NIR-II fluorescence signals could be enhanced when treating with H2O2. HP-H2O2 was subsequently evaluated in murine models of acute lung injury and acute kidney injury. This strategy unlocks the potential of heptamethine cyanines and is applicable to examples with extended conjugation.