A new highly selective and sensitive assay for fluorescence imaging of *OH in living cells: effectively avoiding the interference of peroxynitrite.

A new nonredox fluorescent probe to realize the imaging of hydroxyl radicals (*OH) in living cells was designed and synthesized. The structure comprised the fluorescent dye boron dipyrromethene (BDP) and a 2,2,6,6-tetramethyl-1-piperidinoxyl (TEMPO) unit. This probe could rapidly respond to *OH with a detection limit of 18 pM, and it possessed superior photostability and pH insensitivity. Other reactive oxygen species (ROS) and relevant intracellular components did not interfere. In particular, the important problem of ONOO(-) interference was efficiently avoided. An MTT assay proved that the probe was not very cytotoxic. The probe could penetrate into intact cell membranes to selectively detect intracellular *OH without causing cellular damage in living mice macrophages, normal human liver cells. and human hepatoma cells. These advantageous characteristics make the fluorescent probe potentially useful as a new candidate to detect *OH in broad biosystems.