Molecular Dynamics Simulation Study Of Micro-Nano Glucose Biosensors

Enzymes are highly efficient and specific biocatalyst organisms produced by living cells,playing an irreplaceable important role in life activities.Enzyme biosensors,using enzymes as molecular recognition elements,have the advantages of good selectivity,high sensitivity,fast response,and so on.With the rapid development of biology,chemistry,medicine,physics,microelectronics technology,and other related disciplines,enzyme biosensors have become one of the most active research topics in the areas of biochemical sensors.The enzyme glucose biosensors have been widely studied and benefited hundreds of millions of diabetics all over the world.In the past decades,many researchers focused on improving the sensitivity and stability performance of enzyme biosensors.Especially in recent years,with the development of nanotechnology,scientists have attempted to use various nanomaterials to build or modify electrodes for improving the performance of enzyme biosensors for their high specific surface area,exceptional electrical properties,and so on.However,nanomaterials on biosensors could affect the activity of the enzymes,even could lead to the poor performance of the biosensors.The difficulties of improving the sensitivity of enzyme biosensors should be discussed with two different concepts,which are enzyme immobilization and retaining the activity of immobilized enzymes.The mechanism that how different morphology and electric properties of nanomaterials would have different influences on the behaviors of enzymes is not clear on molecular level.Molecular dynamics simulation has been successfully applied in many areas such as biological physics,biological chemistry,and physical chemistry in recent years.Utilizing molecular dynamics simulation to model and simulate molecules could help to understand the interaction between these molecules on atom resolution.Aiming to solve the uncertain problems on enzyme based biosensors mentioned above,the interactions of different morphology and electric properties of nanomaterials,and glucose oxidase(GOD)and its own cofactor were studied using molecular dynamics simulations,which supplies theoretical guides for the design of high performance biosensors.The main research contents and results are as follows:(1)Molecular simulations of glucose oxidase on nanomaterials with different nanostructures.Assembly of biocompatible nanostructures to retain the enzyme activity and improve the biocatalytic ability is a decisive factor for enhancing the performance of enzyme biosensors.In this study,the effects of two classic biosensor electrode materials with different electrical properties and morphologies and GOD on retaining the enzyme conformation were analyzed by molecular dynamics simulation.First,for the immobilization of GOD,the interfaces of zinc oxide(ZnO)with different electrical properties and 10 nm diameter ZnO nanopore were studied.Then,to simulate the sensing process when electric voltages are applied,positively charged gold planes and 10 nm diameter gold nanopore were investigated as well.The results showed that the nanopore structure was confirmed to be well adapted for the enzyme conformation retaining compared to the plane structure for both ZnO and gold materials,and they almost fit well with the sensitivity measurement results from many previously reported experimental studies.This study also indicates that molecular modeling of the interactions between biomolecules and functional nanostructures is helpful for developing high performance enzyme nanobiosensors.(2)Molecular simulations of FAD immobilized on differently charged single-walled carbon nanotubes.The reconstitution of apo-glucose oxidase(apo-GOD)on single-walled carbon nanotubes(SWNTs)functionalized with the cofactor,flavin adenine dinucleotide(FAD),greatly improved electron transfer turnover rate of the redox reactions in glucose sensing with glucose sensors.Carbon nanotubes can be doped in various ways in actual experiments,which can change the electrical properties of carbon nanotubes.And carbon nanotubes with different electrical properties could affect the conformation changes of FAD,which could compromise the reconstruction of apo-GOD and FAD.In order to find the proper choice of SWNT to achieve the reconstruction,how differently charged SWNT affected the conformation of FAD was studied based on molecular dynamics simulations.Molecular dynamics simulations of FAD functionalized differently charged SWNTs were carried out for 18 ns in an aqueous environment,with counterions to maintain total charge neutrality.The conformation and orientation changes were observed by both trajectory and quantitative analyses.The simulation results showed that in both uncharged and positively charged SWNT situations,FAD adsorbed onto SWNT at the end of the simulations,which increased the steric resistance of molecules and hindered the reconstitution of apo-GOD and FAD to some degree.By contrast,FAD functionalized negatively charged SWNT maintained its original conformation largely.In addition,negatively charged SWNT may be the best choice for electron transfer mediator for the reconstitution of apo-GOD on relay-cofactor units associated with electrodes.(3)For the development of high sensitivity nanobiosensors,this study indicates that how to build biocompatible nanostructures to make enzymes stable should be considered first.Under the enzyme-activity guided strategies,developing well-regulated assembly processes to take the advantage of the high specific surface area inside the nanostructures is an important task to be fulfilled;Molecular modeling and design of the biomolecule and nanostructure hybrid systems can help to develop more exquisite and robust enzyme biosensors.