Application Of Molecularly Imprinted Membrane In The Electrochemical Sensors

Molecularly imprinted polymers (MIPs) are provided with characters such as predetermination, specific recognition and practicability, and MIPs have outstanding advantages such as simple and convenient preparation, robustness in organic solvents and acidic or basic reagents,so MIPs penetrate into the different fields including sensors, membrane separation, solid-phase extraction and catalysis. Because molecularly imprinted membrane (MIM) has the merits of membrane and MIPs, MIM becomes a focus in the field of electrochemical sensors. But the molecularly imprinted membrane is usually thick and highly cross-linked, incomplete template removal, bad reversibility and reproducibility and so on, which limit application of MIM in electrochemical sensors. So studies are encouraged to find new monomers and new methods to extend the molecularly imprinted membrane-electrochemical sensor (MIM-electrochemical sensors). Moreover, preparing novel sensors to imitate the natural molecular recognition in aqueous solution or polar solvent is difficult but useful.This thesis gives a brief overview of the development of the molecularly imprinted technology (MIT) and the application of the MIM in the electrochemical sensors. And two novel MIM-electrochemical sensors are prepared form two different monomers and the characters of the sensors are studied. Further more, the MIPs is synthesized by the in situ polymerization, and investigated the absorption ability and the selectivity by the electrochemical methods.1. A new Schiff base is synthesized from L-cysteine and vanillin, and its structure is characterized by FTIR. The molecularly imprinted membrane is prepared by self-assembling. The gold electrode is immersed in the ethanol-water solution which contains the schiff base and copper(Ⅱ) acetate for 24h, then reacted in dodecanethiol ethanol solution. Finally, the template molecules are removed by 0.1mol/L HClO4. The imprinted membrane is a novel electrochemical sensor for copper ion. Cyclic Voltammetry and A.C. Impedence are used to characterize the modified electrode. Meanwhile, Differential pulse voltammetry is used to study the electrochemical response of copper ion at the modified electrode. The result shows that there is a linear range between the current and concentration of copper ion in 3×10-6～5×10-5 mol/L with a relative coefficient of 0.9972 and the detection limit is 1×10-7 mol/L. The sensor shows high selectivity toward copper ion in the presence of Ni2+, Co2+ and Zn2+.2. Because electropolymerization has some attractive features including the easy adherence of the polymeric films to the surface of conducing electrodes of any shape and size and the ability to control thickness of the films under different deposition conditions, electropolymerization as a novel strategy for preparation of MIM-electrochemical sensors attracts increasing interest in recent years. A novel MIM-electrochemical sensor for salicylic acid (SA) has been synthesized firstly by electropolymerizing o-phenylenediamine on glassy carbon electrode in presence of template molecule (salicylic acid). The insulating property of the polymeric film is investigated by cyclic voltammetry in the 0.5mol/L KCl solution containing 5mmol/L K3Fe(CN)6. Moreover, electrochemical behaviors of SA are investigated in 2×10-4mol/L SA Britton-Robinson buffer. In the first cycle, only an oxidation peak(O1) appears at potential around 1.110V and no complementary reduction peak is observed. However, a reduction peak(R1) is detected at potential around 0.731V. In the second cycle, a new couple peaks are defined at potential 0.730 and 0.778V. The response of the sensor to SA is investigated by square wave voltammetry (SWV). The linearity is obtained over a concentration range of 6×10-5 ~1×10-4 mol/L (R2=0.9961). And the detection limit of SA is about 2×10-5mol/L. The sensor exhibits good selectivity for salicylic acid by virtue of the interaction between molecularly imprinted binding sites and the template.3. Molecularly imprinted polymers are synthesized with salicylic acid as the template, acrylamide as functional monomer and ethylene glycol dimethacrylate as a cross-linker. Moreover, MIPs are tested in the equilibrium binding experiment to analyze the adsorption ability by differential pulse voltammetry. The results show the MIPs have two kinds of binding interaction. The selectivity of MIPs is evaluated by comparing the response to SA with some similar molecular structures like 4-hydroxybenzoic acid; it confirms that the MIPs have a good selectivity of recognition to SA.