Application Of Metal-organic Framework Based On Nickel Bis(Dithiolene) Ligand In Electrochemical Sensing

Metal organic frameworks（MOFs）have interlinked pore structure,uniform aperture,adjustable chemical function in the frame and super high specific surface area.The addition of polyvalent metal nodes or oxidation-reduction active ligands and the embedding of oxidation-reduction active guest molecules in the MOFs pores or channels make MOFs have unique oxidation-reduction activity.Tetrathiafulvalene（TTF）and its derivatives have two reversible electron oxidation states.Its electron delocalization structure is highly conjugated,thermally and photochemically stable,and can be self-assembled with transition metals into MOFs.Studies on the oxidation-reduction activity of metal bis（dithiolene）complexes show that their central[Ni S₄]nuclei have a multi-step reversible oxidation-reduction state,which has been applied in the fields of electricity,catalysis,light,dyes and magnetism.The versatility of metal-disulfide complexes provides a solid basis for their introduction into MOFs.In this paper,three kinds of nanoprobes were prepared and were applied to the field of analysis and detection successfully:1)Nickel-zinc bis（dithiolene）metal organic frameworks was successfully modified by multiwalled carbon nanotubes（MWCNTs）.2)N-doped nickel-manganese bis（dithiolene）metal organic frameworks was combined with reduced graphene oxide（rGO）;3)The L-lysine-functionalized nickel-zinc bis（dithiolene）metal organic frameworks was synthesized with ferrocene modified multi-walled carbon nanotubes（Fc-MWCNTs）.Its specific contents are as follows:Part one:Multiwalled Carbon Nanotubes Modified with Nickel-zinc Bis（dithiolene）Metal-Organic Frameworks for Electrochemical Detection of 5-hydroxytryptamine5-hydroxytryptamine（5-HT）is an important neurotransmitter that would cause a variety of diseases when its concentration varily or exceed certain ranges.Nickel-zinc bis（dithiolene）metal organic frameworks modified multi-walled carbon nanotubes was synthesized successfully and used for detecting 5-HT in this experiment.There is a good coupling between the metal atomic orbital and the ligand orbital of the nickel bis（dithiolene）complex,and the bis（dithiolene）core[Ni S₄]has a definite multi-step reversible oxidation-reduction state.So,the prepared nickel zinc bis（dithiolene）MOFs have good catalytic activity.Under the optimized conditions,the detection concentration range of 5-HT was 0.5-115μM,and the limit of detection（LOD）was0.03μM（S/N=3）.The recovery of 5-HT in urine samples was 99.94%-102.02%,which proved that the sensor had good practical application.Part Two:Electrochemical Determination of Hydroquinone and Catechol by Nitro-Doped Nickel-manganese Bis（dithiolene）Metal-Organic FrameworkHydroquinone（HQ）and catechol（CC）are two isomers of diphenol,widely used in industry and medicine,and are harmful to human health and environmental pollutants.A simple and efficient electrochemical sensor platform for detecting HQ or CC simultaneously based on N-doped nickel-manganese bis（dithiolene）MOF modified by reduced GO was presented.Combined with excellent electrical conductivity of rGO and outstanding catalytic performance of N-Ni Mn-MOF,the prepared N-Ni Mn-MOF/rGO achieves sensitive detection of HQ or CC simultaneously.The linear range was 10-470μM,and the LOD were 0.37μM and0.56μM,respectively.The results showed that the electrochemical sensor constructed in this experiment could be applied to detect HQ and CC in actual water samples.Part three:L-lysine-functionalized Nickel-Zinc Bis（dithiolene）Metal-Organic Framework for Electrochemical Chiral Recognition of Tryptophan EnantiomersL-tryptophan（L-Trp）is an essential component of human and the process of animal protein synthesis,while D-tryptophan（D-Trp）is mainly found in plants and microorganisms.It is rarely found in animals.It is commonly used as an intermediate in the preparation of polypeptide antibiotics and an important precursor of immune drugs.In this part work of the paper,a simple and efficient electrochemical sensing platform based on L-lysine-functionalized nickel-zinc bis（dithiolene）metal-organic framework and ferrocene modified multi-walled carbon nanotubes for the detection of tryptophan enantiomers was prepared.The synergistic effect between Fc-MWCNTs and L-Lys-Ni Zn-MOF makes L-Lys-Ni Zn-MOF/Fc-MWCNTs composites have strong binding ability with L-Trp,and could recognize chiral molecules of different configurations.Under optimized conditions,the sensor detected the enantioselectivity coefficient（I_L/I_D）of 1.866.The peak current has an acceptable linear relationship with the concentration of Trp enantiomers in the range of 2-100μM,and the LOD of L-Trp and D-Trp are 0.4 and 1.3μM,respectively.