Making Metal-organic Frameworks Electron-deficient For Electrochemical Detection Of Dopamine

Dopamine?DA?is an important neurotransmitter in central nervous,renal and hormonal systems.Abnormal DA concentration causes various diseases such as Schizophrenia and Parkinsonism,so accurate determination of DA is important for disease diagnosis and monitoring.Because DA is redox-active,electrochemical detection is the suitable choice.Metal-organic frameworks?MOFs?,a class of porous materials resulting from organic ligands connecting metal-based nodes,have become a vigorous interdisciplinary field of research because their unique diversity and modifiability in structure,porosity and properties are of fundamental interest and allow various potential applications such as gas adsorption,catalysis and sensors.The use of MOFs as electrode modifiers for chemo-and biosensors has emerged rapidly in the last five years but is still in its infancy.Only a few MOFs,usually in combination with other materials,have been used for electrochemical detection of DA,such as Cu?II?,Mn?II?,Al?III?,Cr?III?,Zr-MOFs.Structure-property studies are still lacking,which are necessitated by rational choice and optimization of MOFs.Generally,stronger electrode-analyte interaction can enhance the electron transfer rate for more sensitive voltammetric response.In principle,MOFs can be functionalized to increase the interaction with an analyte,through presynthetic functionalization of organic linkers,or more powerfully,through postsynthetic modification?PSM?of the frameworks.The PSM strategies have been successful in the study of MOFs as absorbents,catalysts,and chemical sensors.Based on the above analysis,UiO-67-DQ was synthesized by postsynthetic N-alkylation of UiO-67-bpy with ethylene ditriflate.the electron-deficient MOF can be used as electrode modifier to design electrochemical sensors for DA because DA contains two electron-rich groups?ethylamine and catechol?and thus should be enriched through CT interactions with the MOF,and hence the voltammetric response is significantly enhanced in favor of sensitive detection.The following is the main research content of our thesis:1.Synthesis and characterization of the electron-deficient UiO-67-DQIn this part,UiO-67-DQ was prepared by postsynthetic N-alkylation of UiO-67-bpy with ethylene ditriflate.We characterized the MOF through a variety methods such as PXRD,FT-IR,¹H NMR,SEM,etc.It turned out that the MOF maintained integrity after post-synthetic modification and there was no significantly change in crystallinity,cage construction and morphology.The modification proportion was calculated by ¹H NMR.2.Electrochemical behaviors for the electron-deficient UiO-67-DQ and electrochemical detection of dopamineIn this part,a three-electrode system was used,UiO-67-DQ was used to modify GCEs,with Nafion?NF?as binder to prevent falling off.The behaviors of DA at different electrodes were investigated by cyclic voltammetry?CV?in phosphate buffer solution?PBS?.At the bare GCE,DA shows reversible redox behaviors,the weak peak currents reflecting the sluggish oxidation of DA.However,UiO-67-DQ/NF/GCE shows obvious increases in both cathodic and anodic currents.The comparison clearly confirms that N-alkylating modification is advantageous to DA-electrode electron transfer.DPV was used to evaluate the performance of UiO-67-DQ/NF/GCE as sensory electrode for quantitative detection of DA.The peak currents?I_p?for C_DA<100?M follow the linear equations I_p??A?=0.121 C_DA??M?+0.112 for UiO-67-DQ/NF/GCE?R²=0.994?and the limits of detection?LOD?is 0.11?M.Co-modification with MWCNTs can further enhance the sensitivity by an order of magnitude?LOD=0.012?M?,illustrating remarkable synergy between the electron-deficient MOFs and the conductive MWCNTs.