Two-photon red-emissive fluorescent probe for imaging nitroxyl (HNO) in living cells and tissues

Nitroxyl (HNO) plays important roles in the regulation of many physiological and pathological processes, and can serve as a potential therapeutic agent for cardiovascular disease. The development of HNO detection in living systems is greatly important for in-depth studies of its biosynthesis and activities. Herein, we describe a novel two-photon red-emissive fluorescence probe (RP) for imaging HNO in living cells and tissues. RP was based on a red-emissive dye, Rho, and showed no fluorescence. When responding to HNO, RP can emit red fluorescence with the emission wavelength at 638 nm. RP exhibited a sensitive and selective response to HNO. Theoretical calculations demonstrated that the overlaps between the HOMO and LUMO were large for Rho and tiny for RP, consistent with the absorption and fluorescence properties of Rho and RP. Assisted by three-dimensional (3D) imaging, the two-photon imaging of HNO with red emission color in living tissues was successfully performed.