A novel carbazolyl GFP chromophore analogue: Synthesis strategy and acidic pH-activatable lysosomal probe for tracing endogenous viscosity changes

Intracellular viscosity changes of the internal microenvironment will lead to many diseases, including cancer, inflammation, neurodegenerative diseases. A novel carbazolyl GFP chromophore analogue Lys-CzFP with acidic pH-activatable was designed for tracing lysosomal viscosity changes. The synthesis developed is a new efficient, novel, one-pot procedure. Lys-CzFP, as a fluorescent molecular rotor, the internal carbazole and benzazole moieties of Lys-CzFP are served as rotators, which could rotate around the single C—C bond in the π-conjugated bridge. Lys-CzFP had a long emission wavelength at 560 nm and a large Stokes shift of 78 nm. The fluorescence intensity of Lys-CzFP exhibited a significant enhancement with increasing viscosity. The fluorescence intensity increased by 98-fold within 5 s from 1.0 cP to 1412 cP, with the fluorescence quantum yield (ϕF) increasing from 0.003 to 0.253 as well as the fluorescence lifetime increasing from 0.25 ns to 1.12 ns, respectively. Furthermore, interference experiments indicated that Lys-CzFP could respond to viscosity particularly. Besides, Lys-CzFP had excellent biocompatibility, low cytotoxicity, and lysosomal localization. Together, Lys-CzFP was successfully applied for tracing endogenous viscosity changes in living cells.