Electrochemical Sensor And Biosensor Fabricated By Molecular Imprinting Polymer Membrane

Molecularly imprinted polymers(MIPs)are becoming an important class of synthetic materials mimicking molecular recognition by natural receptors.The development and application of molecularly imprinted polymeric(MIP)membranes have been the one most attracting assignment in its study.MIP membranes provide synthetic receptors with high selectivity and stability,while electrochemical sensors could offer good sensitivity,at low cost,with possibility of easy design,manufacture, automation and miniaturization.Though the main applications continue to be in the separation field,on the basis of the studies undertaken,it is no doubt that a new generation of MIP membranes -based electrochemical sensors will be established in the future.Limitations exist in functional monomers,cross-linkers and polymerization methods used in traditional imprinting technique.The MIP membranes are usually thick and highly cross-linked,which introduce difficulties for electrochemical sensing application,such as incomplete template removal,broad guest affinities and selectivities,slow mass and charge transfer,high detection limit,bad reversibility and reproducibility,et al.Studies are encouraged to find new imprinting matrices and methods to satisfy the requirements of electrochemical sensing elements.By the way, at present,still little is known about the relative operation mechanism of binding sites, the configuration of the MIPs and the mass transfer mechanism,further investigations are needed,as how to understand the imprinting and recognition process from molecular level.In addition,natural molecular recognition process is always carried out in aqueous solution,however,the imprinting and recognition process in the preceding studies are done mostly in non-polar organic solution.How to use special interactions between molecules to imprint and recognize in aqueous or polar solvent remains to be a difficulty.Hereby,in this dissertation the applications of three kinds of new matrices in molecular imprinting are studied,some of the difficulties associated with traditional matrices are thus overcome,and some new electrochemical sensors are constructed successfully by coupling these imprinted matrices with electric transducers. Preliminary investigation on mechanism of imprinting and recognition process is put up.Extended efforts are also devoted toward imprinting and recognition in aqueous and polar solution.The main content is listed as follows:1.A novel voltammetric sensor has been developed by changing medium based on the molecular recognition of the template by imprinted technology.The sensitive layer has been prepared by electropolymerization of ortho-phenylenediamine and resorcinol on glassy carbon electrode in the presence of the template molecule.Cyclic voltammetry and a.c.impedance studied have been carried out to investigate the properties of the polymeric film.After the template extraction from the resultant solution,re-binding of 2,4-D has been performed from 0.1mol/L H₂SO₄ containing the analyte,and the amount of bonded 2,4-D determined by differential pulse voltammetry.A sensitive response is obtained within 10 min covering a linear range from 1.8×10^-4to 2.0×10^-3mol/L.The sensors so formed possess longer lifetime,better reproducibility(RSD=1.03%)and reversibility.In contrast with traditional electropolymerized membranes,we used the property of sensitive membrane instead of K₃[Fe(CN)₆]as probe,the operation is simple and preparation is easy.The main driving force for recognition is hydrogen interaction.2.A capacitive chemical sensor for theophylline is prepared by electropolymerization of phenol onto the surface of gold electrode.In conjunction with the use of AC impedance measurements,the sensor has been based on the decrease in capacitance caused by the analyte used as the template in the formulation of an electropolymerized molecularly imprinted polymer as receptor layer. Improvement of the insulting properties of the sensor was investigated in detail. Concentration of theophylline up to 1.5×10^-5mol/L could be detected and a detection limit of 1.0×10^-6mol/L.Unlike the capacitive sensors reported in the previous literatures,the present sensors were not treated with alkanethiol after electropolymerization and show even more satisfactory performance.No significant interference was observed from the common structural analog.The sensors so formed possess easily prepared,detection speediness and better reproducibility.The value could reach to 90%of the original when it placed 10 days later(RSD=10%).3.Using acrylamide as functional monomer,N,N'-methylene diacrylamide as the cross linking agent,hypoxanthine as template,molecular imprinted polymer membrane is synthesized in pH=13.5 solution by cyclic voltammetry.The characteristics of the polymer are studied by cyclic voltammetry and a.c.impedence technology.Linear range is 2～15μmol/L and the responding time is 5 min.The sensors so formed possess easily prepared and detection speediness.Comparing with the traditional polyacrylamide,the membrane we prepared has good stability in basic solution.4.Schiff bases and their metallic complexes have been attracted people's interest for a long time owing to its function group of C=N.It can be used as chelator,steady reagent,catalyzer and biological active reagent.Amide is similar to small peptide.It is the model compound of protein enzyme and oxidase and is important to simulating the mechanism of vital process.We synthesized salicyladehyde-cysteine Schiff-base, for the first time,the feasibility of utilizing strong interactions between schiff bases and metal ion to prepare the MIP electrochemical sensor for Cd²⁺,Pb²⁺in aqueous solutions.The imprinted monolayers are composed of two different components,the one is salicyladehyde-cysteine Schiff-base for providing ligand and forming recognition site,the other is 1-dodealkylthiol for obturating the unassembled gold surface.Using Schiff-base as assembling monomer is a new try.Template metal ions are removed quantitatively by 0.10mol/L HClO₄/HNO₃ solution,the reversible recognition site is formed and stable responses are achieved within 3 min.If storing in diluted metal ion solution,the steric direction of the ligands is protected and lateral diffusion is overcome in some extent,the stability of imprinted membrane and recognition site is improved,the sensitivity is higer,so the SAMs could be used more than 100 times.(1)The electrochemical properties of salicyladehyde-cysteine Schiff-base and Cd²⁺were studied in C₂H₅OH/H₂O solution,the constant of stability was calculated.The redox process of Cd²⁺at imprinted electrode was controlled by diffusion.Linear range is 5.00×10^-7～6.00×10^-6mol/Land 6.00×10^-6～6.00×10^-5 mol/L,The optimized ratio of CSA/Cd²⁺is about 2.The imprinted SAMs show high selectivity toward cadmium ion in the presence of Zn²⁺,Co²⁺,Mg²⁺,Ni²⁺,Pb²⁺, Ca²⁺,Fe³⁺.Utilizing the reversible coordinate interaction between central metal ion and amino and carboxyl groups to form recognition site is excellent for ion imprinting and recognition in SAM.(2)The electrochemical properties of salicyladehyde- cysteine Schiff-base and Pb²⁺were studied in C₂H₅OH/H₂O solution,the constant of stability was calculated.The redox process of Pb²⁺at imprinted electrode was controlled by surface reaction.Linear range is 3.00×10^-7～5.00×10^-5mol/L,the optimized ratio of CSA/Pb²⁺is about 2.The imprinted SAMs show high selectivity toward lead ion in the presence of Zn²⁺,Co²⁺,Mg²⁺,Ni²⁺,Cu²⁺,Fe³⁺.The properties of MIP membrane,response mechanism of electrode,selectivity,reproductivity, reversibility and life were all investigated.5.Using the polyvinylidene fluoride microporous membrane as the supported membrane and Zinc(â…¡)-quercetin complex as template,the molecularly imprinted polymer membranes were synthesized through in-situ polymerization by UV irradiation.The imprinted membranes have a lot of strongpoints:The space configuration is special because of forming metal complex,the selectivity for template is higher.Comparing with nubby or dubbed MIPs,it is not only overcome the shortcoming of longer polymerization time and requiring screen for but also shorten the washing time.The selectivity for structural analog-rutin was also studied. The imprinted membranes exhibited selective permeation for quercetin in certain Zinc(â…¡)acetate solution through permeation binding experiment.The influences of cations and anions on the selective permeation of imprinted membranes were investigated.It will be helpful for the separation and enrichment of quercetin in herbal medicine.