Electrochemical Sensing Surface Fabricated By Molecular Imprinting Techniques

Molecularly imprinted polymers (MIPs) are becoming an important class of synthetic materials mimicking molecular recognition by natural receptors. MIPs provide synthetic receptors with high selectivity and stability, while electrochemical sensors could offer good sensitivity, at low cost, with possibility of easy design, manufacture 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 MlPs-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 MIPs 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 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 succesfuly 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. We have investigated for the first time on the formation of imprinted recognition sites in electro-synthesized films based on mercaptan assemblies and the fabrication of MlPs-based electrochemical sensors for electro-active polutantnitrobenzene and electro-inactive drug cinchonine. Compared with traditional electro-synthesized polymer films, the imprinted electro-synthesized film based on mercaptan assemblies put up higher stability, in particular against brushing off and nice resistance toward harsh treatments. (1) The electrode process for nitrobenzene on the imprinted films is a traditional CrEi mechanism. A sensitive response is obtained within 2 min covering a linear range from 5.00x10-5 to 4.50x10-3mol/L. Electrochemical degradation is put forward for the first time to remove the template molecule nitrobenzene, which avoid the possible damage toward imprinted films and recognition sites brought by mechanical washing and solvent extraction. The sensors so formed possess longer lifetime, better reproducibility (RSD=2.5%) and reversibility. (2) For electro-inactive cinchonine, an indirect, fast measurement is carried out by chronoamperometry using potassium ferricyanide as an electro-active probe. Stable response is achieved within 4 min, covering a linear range from 5.00x10-6 ~4.00xl0-5 mol/L, with a detection limit of 1.50xl0-7mol/L. The main driving force for recognition is hydrophobic interaction and complementary cavity effect.2. Extensive efforts have been devoted to the preparation of imprinted recognition sites in self-assembled monolayers (SAMs) and the coupling of these materials with electric transducer to fabricate electrochemical sensors for L-/D-serine and for mercury, copper and lead ions. Forming recognition sites in SAMs decreases the d...