Making metal–organic frameworks electron-deficient for ultrasensitive electrochemical detection of dopamine

Two metal–organic frameworks (MOFs) containing bipyridinium moieties, UiO-67-MQ and UiO-67-DQ (MQ = N,N′-dimethyl-2,2′-bipyridinium, DQ = N,N′-ethylene 2,2′-bipyridinium), prepared by post-synthetic N-alkylation of the Zr-MOF with 2,2′-bipyridyl-4,4′-dicarboxylate (UiO-67-bpy, bpy = 2,2′-bipyridyl), were used as electrode modifiers for detection of dopamine. Compared with UiO-67-bpy, UiO-67-MQ and UiO-67-DQ significantly enhance the voltammetric sensitivity of dopamine, which is attributed to the donor–acceptor interactions between the electron-deficient bipyridinium moieties and the electron-rich analyte. The detection limits are further lowered by an order of magnitude by the introduction of multi-walled carbon nanotubes, demonstrating remarkable synergy in promoting electron-transfer kinetics. This work is the first report of the use of electron-deficient MOFs in electrochemical sensors.