Construction Of Graphene-based Nano-Assembly For Enzyme Immobilization

Graphene,a two-dimensional（2D）nanosheets,has attracted a lot of attention in enzyme immobilization owing to its remarkble physicochemical properties.Graphene nanosheets could offer numerous binding sites to enzyme as carries,for constructing high-performance biocatalytic systems.However,the graphene sheets are nanoscale,leading to difficulty in recycling of immobilized enzymes.Bioadhesion and biomimetic mineralization are commonly used methods for preparing immobilized enzyme,which could grow different nano coatings under normal pressure,temperature and neutral pH.In this study,different three-dimensional（3D）graphene-based nano-assembly were prepared via bioadhesion and biomimetic mineralization.Assembling of graphene into graphene-based nano-assemblies from GO sheets could confer it high surface area for loading enzyme.The monolithic size and strong interaction between coating and enzyme make it possess recyclability and high stabilities.The details in this study are summarized as follows:Firstly,dopamine was used to modify GO by bioadhesion for preparing P-rGO nanosheets.Candida rugose lipase（CRL）was binding on the surface of P-rGO via physical adsorption and covalent interaction.P-rGO nanosheets exhibited high specific surface area and the loading capacity of CRL was as high as 642.5 mg g^-1.The P-rGO also showed better recycling,thermal and pH stabilities.The covalent interaction between amino on CRL and catechol groups at PDA could efficiently reduce the leaching and comformational change of CRL.Secondly,ZIF-8 nanoparticles was used to regulate surface wettability of P-rGO,and then assembling it onto oil-water interface to form stable microcapsule-type graphene-based nano-assembly.The immobilization efficiency can reach up to65.0%⁶8.1%,owing to physical adsorption between ZIF-8 and CRL as well as covalent interaction between catechol groups on PDA and amino on CRL.The loading capacity could reach 340.3⁴87.6 mg g^-1.This graphene-based nano-assembly could stably exist in oil/water system,and retain 50%of initial enzyme activity after recycling for 6 times.Thirdly,PEI was used to assemble GO into foam-type graphene-based nano-assembly.CRL was adsorpted onto the surface of rGO/PEI,which induced the process of biomimetic mineralization to synthesize ZIF-8 coating.The loading capacity of rGO/PEI/CRL could reach up to 656.0 mg g^-1,the activity recovery could reach 40.0%.ZIF-8 coating could efficiently restrain leaching and comformation change of CRL.The foams-type graphene-based nano-assembly shown good stability in solvent and high temperature.The nano-assembly could retain 68%and 40%of initial activity after treated by 50%DMF for 1 h and at 70 ^oC for 2 h,respectivly.What’s more,it could retain 92.1%of the initial activity after recycling for 6 times.