Reengineering Cyanine Dyes via Borondifluoro Indolenine: A Tunable Platform for Wash-Free Imaging and Responsive Biosensing

Fluorescent probes are essential tools for visualizing biological processes, yet conventional cyanine dyes suffer from limited structural flexibility, poor photostability, and weak compatibility with wash-free imaging. Here, we introduce a modular, neutral BF2-bridged cyanine (BCy) platform by re-engineering the indolium scaffold with a borondifluoro indolenine (BFI) fragment. BCy dyes exhibit high brightness (up to 12.4 × 104 M-1 cm-1), robust photostability, and emissions spanning 588-837 nm. The tunable BFI moiety enables the construction of wash-free, far-red/NIR probes for the plasma membrane, lipid droplets, mitochondria, and lysosomes as well as pH- and H2O2-responsive sensors. These probes support high-contrast multicolor and STED imaging, as well as dynamic organelle tracking in live cells and a mouse model of liver injury. This work establishes BF2-cyanines as robust scaffolds for next-generation fluorophores in advanced bioimaging and biomedical diagnostics.