Metal-organic Framework For Electrochemical Detection Of Neurotransmitters

Neurotransmitters?NTs?,as chemical messengers,control the behavior and physiological functions of central and peripheral nervous systems.Its abnormal content will cause a series of diseases related to nervous system,such as Parkinson's disease,Alzheimer's disease and schizophrenia.Therefore,it is very important to identify and monitor NTs.How to detect NTs conveniently,quickly and sensitively has become the focus of researchers.Because of their unique advantages,electrochemical sensors are still considered to be the most effective and convenient detection methods.Metal-organic frameworks?MOFs?are new kind of porous coordination polymer composed of metal ions or ion clusters and organic ligands.Because of the large specific surface,the diversity and adjustability of structure and properties,MOFs has been used as electrode modifier and applied in the field of electrical analysis.Usually,conductive materials including carbon materials?graphene,carbon nanotubes,graphite powder,etc.?,noble metal materials and polymers,etc.are composited with MOFs so as to improve the detection sensitivity through synergistic effects.The related reports involve human health,environmental protection and public safety,including the detection of bio-molecules,drugs,heavy metals and explosives.However,most reports are limited to the phenological descriptions of the phenomena and results.The systematic studies on the interaction mechanism and the relationship between structure and performance are still lacking.Based on the above analysis,this thesis investgate two types of MOFs:1)The Zr₆-carboxylate-based MOFs,including UiO-67 and UiO-67-bpy with biphenyl and 2,2'-bipyridyl?bpy?as intercluster links,respectively;2)MIL-101,including MIL-101 and sulfo-MIL-101.The MOFs were used to detect norepinephrine?NE?and dopamine?DA?respectively.The comparative studies with the isostructural MOFs can help us to gain a deep understanding of the structural-performance relationships.The studies prove that the hydrogen bond formed between MOFs?pyridine nitrogen and sulfonic acid group?and analyte was conducive to the enrichment of analyte on the electrode surface,thus lowering the detection limits.The thesis is devoted to the following two subjects.1.Synergistic effect between a bipyridyl-functionalized MOF and graphene for sensitive electrochemical detection of NEGO-UiO-67-bpy/GCE,was fabricated by casting a mixture dispersion of UiO-67-bpy?a Zr-carboxylate MOF derived from 2,2-bipyridyl-5,5-dicarboxylate?and GO onto a GCE.The continuous cyclic scanning in the range from 0 to-1.6 V?vs.Ag/AgCl?caused irreversible reduction of GO and reversible redox of bpy?around-0.93 V?,and produced the target electrode?ERG-UiO-67-bpy/GCE?.Comparative studies with ERG/GCE and UiO-67-bpy/GCE indicate that UiO-67-bpy and ERG in ERG-UiO-67-bpy/GCE should have some kind of synergetic effects rather than a simple additive effect in enhancing the voltammetric response to NE,but the composite shows negative effects on the response to DA and catechol.The composite electrode was further compared with the counterpart?ERG-UiO-67/GCE?fabricated from an isostructural bipyridyl-free MOF?UiO-67?.The results reveal that the bipyridyl moiety in UiO-67-bpy plays an important role in promoting the synergetic effects.It is proposed that electron transfer should mainly occur between the redox-active o-dihydroxylbenzene group and the ERG rather than the MOF,because the insulative MOF cannot transport electrons.The hydrogen bonds between the bipyridyl moiety and the 2-aminoethanol moiety of NE serve to adsorb the analyte molecules on the electrode surface and meanwhile bring the dihydroxylbenzene group of NE close to ERG in favor of electron transfer.For DA and CA,which have no 2-aminoethanol moiety,the hydrogen bonding interactions between bipyridyl and the two hydroxyl groups dominate,which keep the dihydroxylbenzene group from ERG to the disadvantage of electron transfer,so the incorporation of the MOF has a negative effect.For ERG-UiO-67/GCE,there is no effective hydrogen bonding between the MOF and NE,and the MOF just serves to enlarge the surface area for preconcentration of NE,leading to limited enhancement of the electrochemical signal.Under the optimized conditions of electrode preparation and DPV measurement?the amount of UiO-67-bpy,the thickness of composite material on the electrode surface and the pH of electrolyte?,UiO-67-bpy and graphene play a strong synergistic role.When the analyte concentration is 0.2-100?M,a good linear relationship between peak current intensity and NE concentration can be wrote as:I_pa??A?=0.74[NE]+0.52?R²=0.996?,and the detection line reaches 27 nM.In addition,when urea acid and NE coexist,almost no interference is present in the detection of NE,and both of them can be detected at the same time with good linear relationship and sensitivity.The application of ERG-UiO-67-bpy/GCE in practical samples?urine sample?also achieved good results,and the electrode showed good stability and repeatability.2.Applying sulfonate-functionalized MOF to high-performance electroanalysis of dopamineBased on the successful experience of the above work,we synthesized another type of MOF?MIL-101,sulfo-MIL-101?via solvothermal method to detect dopamine.The graphite paste electrodes?MIL-101-GPE and sulfo-MIL-101-GPE?were prepared by MOF and graphite powder,which could play a synergistic role.The electrode surface charge transfer resistance,the effective surface area and the peak current of CV all show that sulfo-MIL-101-GPE is superior to MIL-101-GPE in the electrochemical behavior of dopamine.Sulfonate groups provide open sites for DA adsorption through electrostatic interaction and hydrogen bonding,which is conducive to electron transfer.Therefore,sulfonate modified MOF can significantly improve the electrocatalytic performance of DA.This work is helpful to understand the relationship between the structure?functional groups?and electrochemical performance,and provides a new idea for the design of electrochemical sensors using the versatility and tailorability of MOFs.The linear relationships between CV peak current intensity and DA concentration are:I_pa??A?=0.281[DA]-0.023?R²=0.998?and I_pc??A?=0.214[DA]+0.096?R²=0.992?,the concentration range of analyte is 0.2-100m?44?and 0.07-100?M respectively,the detection limit?LOD?is 43 nM,and the sensitivity is 2.55?A?M^-1 cm^-2.The electrode sulfo-MIL-101-GPE shows satisfactory results in terms of anti-interference,repeatability and stability.In addition,it can also be used for quantitative analysis of dopamine in the actual sample of medical dopamine injection?dopamine hydrochloride injection?.