Red emission fluorescent probes for visualization of monoamine oxidase in living cells

Here we report two novel red emission fluorescent probes for the highly sensitive and selective detection of monoamine oxidase (MAO) with large Stokes shift (227 nm). Both of the probes possess solid state fluorescence and can accomplish the identification of MAO on test papers. The probe MAO-Red-1 exhibited a detection limit down to 1.2 μg mL−1 towards MAO-B. Moreover, the cleavage product was unequivocally conformedby HPLC and LCMS and the result was in accordance with the proposed oxidative deamination mechanism. The excellent photostability of MAO-Red-1 was proved both in vitro and in vivo through fluorescent kinetic experiment and laser exposure experiment of confocal microscopy, respectively. Intracellular experiments also confirmed the low cytotoxity and exceptional cell imaging abilities of MAO-Red-1. It was validated both in HeLa and HepG2 cells that MAO-Red-1 was capable of reporting MAO activity through the variation of fluorescence intensity.