A triarylboron based two-photon fluorescent probe for the detection of intracellular Monoamine oxidase by a reaction-induced aggregation

Monoamine oxidases (MAOs) play vital roles in maintaining the homeostasis of biogenic amines by catalyzing their oxidation to the corresponding aldehydes. Recent studies have suggested that MAOs can be effective biomarkers for certain neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. To elucidate their distinct roles in different diseases, their selective detection is essential. In this study, we functionalized triarylboron compounds with the hydrophilic cyclen group, to develop novel fluorescent probe for detecting MAOs. TAB-1, TAB-2 and TAB-Br were synthesized, the hydrophilicity of the molecule was tuned by varying the number of diphenylamine and cyclen groups introduced into the structure. TAB-1 and TAB-2 exhibited significantly enhanced fluorescence in the presence of MAO A or MAO B. This is because their hydrophilic and flexible cyclen groups can be oxidized by MAOs to more hydrophobic and rigid molecular structure, which can reduce energy dissipation resulting from intramolecular motion. TAB-2 exhibit a more obvious aggregation phenomena than TAB-1 and a blueshift in the fluorescence spectra, thus allowing a ratiometric readout. Moreover, such a mechanism also provides a rapid response speed for MAOs. The introduction of TAB-2 into different live cells showed that it could differentiate the cells overexpressing MAO from other cells.