DDAO is a promising near-infrared (NIR) red fluorescent probe with long emission wavelength (λem = 656 nm) and tunable excitation wavelength (600-650 nm). It can de desiged for detection of the activities of different enzymes such as β-galactosidase, sulfatase, protein phosphatase 2A, carboxylesterase 2, human albumin and esterases.