Construction Of Polysaccharide Metal-organic Framework-enzyme Complex And Its Application

Metal-organic frameworks(MOFs)are widely used in gas storage and separation,drug delivery,biocatalysis and other fields due to their porosity,large specific surface area and stable structure.At present,the in-situ synthesis method of imbedding enzyme molecules to construct metal-organic framework-enzyme complexes have been a focus in recent years.This method can significantly improve the stability of the enzyme,and there is no requirement on the size of the enzyme molecule,which has good versatility.However,the MOFs suitable for this method are mainly microporous ZIFs materials,which have high mass transfer resistance and low apparent activity of the enzyme after embedding(<5%).At the same time,immobilized enzyme activity was affected by high concentration of imidazole organic ligands during the preparation process,which decreased more than 70%.In this study,water-soluble polysaccharide macromolecules were introduced into the structure of MOFs as mixed ligand components.The enrichment of metal ions by polysaccharide molecules was used to regulate the crystal growth process of MOFs,thus reducing the amount of imidazole organic ligands in the preparation process and reducing the damage to enzyme molecules.Meanwhile,the steric hindrance structure of polysaccharide macromolecules introduced mesoporous into MOFs,which significantly promoted the mass transfer in the enzyme catalysis process and improved the apparent activity of enzyme.Therefore,this paper first explored the preparation of polysaccharide MOFs with the polysaccharide macromolecules as mixed ligand components,and further used it as the carrier of the immobilized enzyme to explore the influence of polysaccharide MOFs on the activity and stability.On this basis,polysaccharide MOFs immobilized enzyme biosensor was constructed and used for the determination of phenol content in aqueous solution.In this research,a series of micro-mesoporous polysaccharide MOFs with different polysaccharide molecules as mixed ligands were constructed by introducing polysaccharide biomacromolecules into the synthesis process of MOFs and regulating the growth process of MOFs based on their metal ion enrichment characteristics.Scanning electron microscopy,transmission electron microscopy,X-ray diffraction,infrared spectroscopy,nitrogen adsorption curve and other characterization methods proved the effectiveness of this strategy.The constructed polysaccharide MOFs have the same crystal structure as the original MOFs,and contain micro-mesoporous structure,which can promote the transfer of macromolecules.On this basis,polysaccharide MOFs-enzyme complexs were further prepared by in-situ aqueous phase synthesis.By introducing enzyme molecules into the synthesis process of polysaccharide MOFs,a variety of polysaccharide MOFs-enzyme complexs catalysts with high activity and stability were successfully constructed by in-situ synthesis method.Compared with the MOFs-enzyme complexs,the apparent catalytic activity of the prepared polysaccharide MOFs-enzyme complexs were increased by 3?67 times,and the maximum reaction rate were increased by 20?145 times,which significantly improved the catalytic efficiency.At the same time,polysaccharide MOFs provided a protective effect for the embedded enzyme molecules,and the stability was significantly improved.Compared with natural enzymes,polysaccharide MOFs-enzyme complexs catalysts retained about 40%activity under extreme conditions such as high temperature and organic solvents,while the activity of free enzymes remained less than 5%.Meanwhile,the catalytic activity of polysaccharide MOFs-enzyme complexs catalysts remained about 70%after 5 times of repeated use.Furthermore,in this paper,polysaccharide MOFs-tyrosinase complex biosensor was constructed by modifying the polysaccharide MOFs-tyrosinase to glassy carbon electrode for the detection of phenol content in aqueous solution.The electrochemical performance of polysaccharide MOFs-tyrosinase modified electrode was studied by cyclic voltammetry.When the concentration of phenol was in the range of 0.4 to 0.8 mmol/L,the reduction current of the system showed a good linear relationship with the concentration of phenol,the linear equation was I_PC(?A)=-5.797C(mmol/L)-0.597,the correlation coefficient R²=0.983.The limit of detection was 0.03 mmol/L(S/N=3),and the sensitivity was 82.01m A·mol^-1·cm^-2.At the same time,the detection system has good reproducibility,stability and anti-interference.This system is also suitable for the concentration determination of catechol and hydroquinone.In this research,the polysaccharide MOFs with micro-mesoporous structure and polysaccharide MOFs-enzyme complex catalytic systems were constructed.Furthermore,the application of polysaccharide MOFs-enzyme complex in biosensors was explored,which provided theoretical reference and research basis for the further study of the construction and application of biological macromolecule MOFs.