Aminophenyl fluorescein solution, also known as APF, is a novel fluorescent probe. APF exists as a non-fluorescent entity, which converts to its fluorescent form called fluorescein upon oxidation. The excitation length is at 488nm, and the emission spectrum is monitored between 495-600nm and measured using flow cytometry.

Fluorescence intensity increases after reaction with hROS (e.g. hydroxy radical, peroxynitrite and hypochlorite). And, APF is resistant to light-induced autoxidation.

Aminophenyl fluorescein solution is a suitable tool to detect hypobromous acid (HOBr) produced in eosinophils. It is used to detect the halogenating activity of heme peroxidases in leukocytes. APF does not react with nitric oxide, superoxide, and hydrogen peroxide; hence, it can be used to detect peroxynitrite differentially.

Fluorescent detector of highly reactive oxygen species (hROS). Fluorescence intensity increases after reaction with hROS (e.g. hydroxy radical, peroxynitrite and hypochlorite). Since APF does not react with nitric oxide, superoxide, and hydrogen peroxide, it can be used to differentially detect peroxynitrite. APF is resistant to light-induced autoxidation.