Catecholamines, such as dopamine and L-dihydroxyphenylalanine (L-DOPA), are associated with different physiological functions and diseases. In our recent studies, a novel water-soluble boronic acid compound 3c was identified as a selective fluorescent sensor for L-DOPA. This compound not only has the ability to interact with dopamine and catechol, but also has no fluorescence intensity change for L-DOPA precursors in vivo, such as L-tyrosine.