Synthesis Of Novel Ionic Liquids,Their Effect On Enzyme Activity And Application In Glucose Biosensors With Nanomaterials

With the development of green chemistry,raw materials for synthesis of ionic liquids and their toxicity have attracted much attention of researches.The main strategy for sustainable development is to synthesize biobased ionic liquids derived from biocompatible materials.Moreover,the design of biocompatible ionic liquids to reduce their potential environmental hazards is also a hot topic in ionic liquids research.The influence of ionic liquids on enzyme activity is one of the indicators reflecting their biocompatibility.Glucose biosensor uses glucose oxidase as recognition element to detect glucose,which has the advantages of low detection limit,convenient application and rapid response.It is of great scientific significance to develop new strategies to prepare glucose biosensor to meet the demand of analytical samples in various fields.In this thesis,a series of biobased ionic liquids based on tropine and amino acids were synthesized using tropine,hydrolysate of natural hyoscyamine as the cation core and amino acids as anion.The effects of these ionic liquids on lipase and glucose oxidase activities were studied.In addition,the application of these ionic liquids and nanomaterials in glucose biosensors were also explored.The main contents and results are as follows:（1）Tropine-amino acid based ionic liquids（[Bu Tr][AA]ILs）were prepared by bromobutane modification,anion exchange and acid-base neutralization.Afterwards their structures and thermal stability were characterized with Fourier transform infrared spectroscopy（FT-IR）,nuclear magnetic resonance spectra(¹H NMR and ¹³C NMR),mass spectrum（ESI-MS）,and thermogravimetric analysis（TG）.Then the basic physical properties of[Bu Tr][AA]ILs were measured involving density and conductivity,which can provide essential data for their application.（2）In order to systematically investigate the effect of tropine-amino acid based ILs on enzyme activity,ILs of tropine with different carbon chain length as cation core and serine as the anion（[Cn Tr][Ser]ILs）were synthesized.The p H and critical micelle concentration of tropine-amino acid based ILs aqueous were measured and the effect of these ILs with different concentrations on the activities of lipase and glucose oxidase（GOx）were investigated.It was found that ILs with polar amino acids as anions could maintain80%activity of lipase at concentration of 0.5 M.The longer the carbon chain length of the ILs is,the greater the inhibitory effect on lipase activity has.ILs which anion is polar and negatively charged amino acid can improve the activity of GOx at the concentration of 0.3M.Moreover,ILs with a longer carbon chain has a better effect on promoting GOx activity at a certain concentration.In addition,ultraviolet spectrum,fluorescence spectrum,Fourier transform infrared spectroscopy,circular dichroism and molecular docking were used to further illustrate the interaction between ILs and enzyme.（3）A new glucose biosensor was prepared by combining the advantages of tropine-amino acid based ILs,metal nanomaterials and carbon nanomaterials.The effects of ILs with different anions,carbon chain lengths,concentration and Ag/multi-walled carbon nanotubes（Ag/MWCNTs）content on the active area of the electrode were investigated.Among them,[Bu Tr][Ser]/Ag/MWCNTs has the largest active area of modified electrode,which is 1.68 times larger than that of the bare electrode.As the carbon chain length of the N⁺is greater than 4,the active area shows a downward trend.The electrode was modified with 5mg/m L of GOx and was finally determined glucose in PBS with p H of 7,at a working potential of-0.45 V and 25°C after investigating the influence of the test conditions and the amount of enzyme on the biosensor performance.Besides,the GOx coverage of the modified electrode is 2.16×10^-9 mol/cm²,the electron transfer rate k_s is 0.91 s^-1,and Michaelis-Menten（）is 5.10 m M.The glucose detection range of the[Bu Tr][Ser]/Ag/MWCNTs/GOx/GCE biosensor is 20μM～1.82 m M,the sensitivity is 33.50μAm M^-1cm^-2,and the detection limit is 13.59μM（S/N=3）.Furthermore,the biosensor has good anti-interference ability,reproducibility,repeatability and stability.And the test results are satisfied in actual honey samples,indicating that it has the potential for application in glucose detection in the food industry.（4）A novel enzymatic biosensing platform toward glucose is achieved with nanocomposite of Fe₃O₄-chitosan-β-cyclodextrin（Fe₃O₄-CS-CD）and MWCNTs.The synergistic effect of magnetic nanoparticles and MWCNTs can improve the impedance of the electrode and promote electron transfer.In addition,the electrode can maintain the biological activity of GOx and exhibit direct electron transfer from enzyme to electrode.The electrode with 3 mg/m L of modified material and 5 mg/m L of GOx has shown good response to glucose at 25°C in PBS（p H=7）by optimizing the conditions of the electrode preparation and test.The coverage of GOx on the modified electrode is 3.69×10^-10mol/cm²,and the electron transfer rate is1.73 s^-1.The glucose detection range of the Fe₃O₄-CS-CD/MWCNTs/GOx/GCE biosensor is 40μM～1.04m M,the detection limit is 19.30μM（S/N=3）,and the sensitivity is 23.59μAm M^-1cm^-2.The biosensor has good anti-interference ability,reproducibility,repeatability and stability.Besides,the practical application of the biosensor was test in human serum samples with satisfactory accuracy,demonstrating promising and practical potential in biomedical diagnostics.