Elevated homocysteine (Hcy) has been considered as a risk factor for vascular and renal diseases. Therefore, the development of Hcy-specific fluorescent probes, especially ratiometric fluorescent probes is of great importance. In the present study, a highly Hcy selective ratiometric fluorescent probe 3-(benzo[d]thiazol-2-yl)-2-hydroxy-5-methyl-benzaldehyde (BA), based on an ortho-hydroxy aldehyde functionalized benzothiazole, is presented. The probe responded selectively to Hcy over other tested species including Cys and GSH with ratiometric fluorescence changes. The probe possessed itself green fluorescence (λ_em=544 nm). Addition of Hcy to the BA solution triggered remarkable blue fluorescence (λ_em=478 nm). The fluorescence intensity ratios (I_{478 nm}/I_{544 nm}) were linearly related to the amounts of Hcy from 0 to 1.0 mmol/L with a detection limit of 1.6 μmol/L. The probe BA possessed low cytotoxicity and desirable cell permeability, and could be employed for the ratiometric imaging of Hcy in living cells, suggesting its potential applications in biological systems. Moreover, the sensing mechanism of BA for Hcy was verified by NMR, HRMS and time-dependent density function theory calculations.

Key words: homocysteine, ratiometric, fluorescent probe, cell imaging