Application Of Molecularly Imprinted Membrane In The Electrochemical Sensors

Molecular imprinting technology （MIT） is a new technique for preparingspecialized recognition media. The basic principle is that the imprinting templatemolecules, functional monomer and cross-linking agent were dissolved in a solvent,and were having complementary functional polymerization. After extracting thetemplate molecules from the polymer, the polymer leaves cavities inside the polymerswhich are complementary in terms of size, shape, and functional groups orientation tothose of the template molecules. Thus, it is shown specific selectivity and adsorptioncapacity of the template molecules. The technique has been applied in many fieldswidely. With the characteristic of predetermination, recognition and practicability,MIPs are used in many fields, such as chiral separation of enantiomer and isomer,clinical drug analysis, enzyme-minic catalyzed reaction, solid phrase extraction,chemical bionics sensor and film separation. In particular, molecularly imprintedmembrane has both advantages of the membrane and molecular imprinted polymer, sothat molecularly imprinted membrane is becoming the hot topic of research in the fieldof electrochemical sensors. But the molecularly imprinted membrane is usually thickand highly cross-linked, incomplete template removal, reproducibility, bad reversibilityand so on, which limited application of molecularly imprinted membrane inelectrochemical sensors. So studies are encouraged to find new monomers and newmethods to extend the molecularly imprinted membrane-electrochemical sensor.This paper gives a brief overview of the development of the molecularlyimprinted technology （MIT） and the application of the molecularly imprintedmembrane in the electrochemical sensors. And three novel molecularly imprintedmembrane electrochemical sensors are prepared form different monomers and thecharacters of the sensors. Furthermore, the MIPs are investigated the ability of druganalysis by the electro-chemical methods.1. Molecularly imprinted polymers are synthesized with salicylic acid as thetemplate, and pyrrole as functional monomer. The template could be removedeffectively by a two-step method. The first step was fixed potential peroxide and thesecond step was alkali solution washing. Moreover, MIPs are tested inthe electrochemical study by cyclic voltammetry and differential pulse voltammetry. The selectivity of MIPs is evaluated by comparing the response to SA with somesimilar molecular structures, and it confirms that the MIPs have a good selectivity andsensitivity for recognition to SA. The imprinted sensor could be easily fabricated andshowed a stable and reproducible response without any influence of interferentscommonly existing in drug combination samples. Under the optimum conditions,salicylic acid concentrations of1.0ⅹ10^-3-5.0ⅹ10^-9mol·L^-1within the framework of itspeak current showed a good linear relationship, with the linear regression equationi_pa=18.3602-2.2110lgC (mol·L^-1), correlation coefficient r=0.9979. The detection limitof the sensor was3.5ⅹ10^-10mol· L^-1（S/N=3）.2. A sensitive amperometric sensor for norfloxacin was introduced. The receptorlayer was prepared by molecularly imprinted photopolymerization of acrylamide andtrimethylolpropane trimethacrylate on the surface of gold electrode. The bindingmechanism of molecularly imprinted polymer was explored by ultraviolet spectrum（UV） and infrared spectrum （IR）. The chemosensors were characterized by cyclicvoltammetry（CV）, differential pulse voltammetry （DPV） and scanning electronmicroscopy. The MIP electrode showed very high recognition ability in comparison toNIP. Some parameters affecting sensor response were optimized. Binding of analyseswas detected by measurements of amperometric i-t curve. The linear regressionequation i_pa=1.4406-0.3240lgC (mol·L^-1), correlation coefficient r=0.9949. At thesame time, the NFXC concentration of1.0×10^-9mol· L^-1also could be detected with adetection limit of3.5×10^-10mol· L^-1（S/N=3）.3. Molecularly imprinted polymers are synthesized by a two-step method. Thefirst step was prepared MWNTs to be modified in electrode, and the second step waselectrochemical polymerized with cobalt nitrate as the template, and pyrrole asfunctional monomer. Moreover, MWNTs-MIPs are tested in the electrochemical studyby cyclic voltammetry and AC impedance. The selectivity of MWNTs-MIPs isevaluated by comparing the response to Co²⁺with some similar molecular structures.Analysis of Co²⁺was detected by measurements of cyclic voltammetry. A widedynamic linear range of2.0×10^-6to2.0×10^-7mol·L^-1was obtained, and the linearregression equation i_pa=-4.9644-1.0349C(10^-6mol/L), correlation coefficient r=-0.9975.