The Research And Application Of Electrochemical Sensors Based On Films Of Molecularly Imprinted Polymers

Molecular imprinting belongs to the category of host-guest chemistry in super-molecule chemistry. It is an interdiscipline subject, which origins from macromelocular chemistry, biochemistry, material chemistry, etc. Molecular imprinted polymers (MIPs) are such a synthetically man-made receptor: it owns the cavities which match up substrate molecules in space and can recognize the substrate molecules through the ordered functional groups. Compared with the routine and traditional medium used for separation and analysis, the outstanding character of MIPs based on molecular recognition is its excellent selectivity to the substrates. Further more, MIPs are highly stable and able to bear high temperature, high pressure, acid or alkaline condition, and organic solution. Due to their predetermination, specific recognition and practicability, MIPs have been largely put into use in catalysis, material chemistry, separation and biomimic sensor. While electrochemical sensors are highly sensitive and made at low cost, with possibility of easy design, manufactory and miniaturization, it is no doubt that a new generation of MIPs-based electrochemical sensors will be established in the future, on the basis of the studies undertaken. The MIPs made in traditional ways 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, etc. In addition, the imprinting and recognition process in the previous studies are done mostly in non-polar organic solution. How to use special interactions between molecules to imprint and recognize in aqueous or polar organic solution remains to be a difficulty. Hereby, three novel materials have been used to prepare recognition sites for four organic compounds based on the excellent charactererization of MIPs in this thesis. These MIPs have been put into use as sensitive elements to construct bio-mimetic sensors. The analytic objects deal with pharmaceutic molecules and environmental contaminations. Not only these noval materials have conquered the inherent shortcomings of traditional MIPs in some part, but also imprinting and recognition process have been achieved in aqueous solution. Details are presented in this thesis as follows: 1. An attempt has been made to combine molecular imprinting technique and the electropolymerization of self-assembled o-amino thiophenol (o-AT) to prepare imprinted film using cinchonine as the template analyte. The procedure of forming recognition cavity and the effect of the ratio of monomers to templates on the imprinted film, together with sensitivity and selectivity to cinchonine on the imprinted electrode, are demonstrated. An indirect and rapid detection is carried out using potassium ferricyande as a probe. Stable response is achieved within 4 min, covering a linear range 5.00 × 10-6 ~ 4.00 × 10-5 M, with a detection limit of 1.50 × 10-7 M. From the results, the main driving force for recognition is supposed to be hydrophobic interaction, complete cavity effect and π-πinteractions between phenyl group of monomers and the enaphthyl group of cinchonine. 2. Selective recognition of benzenediol isomers is realized using molecularly imprinted SAMs formed through spreader-bar approach. The surface of the imprinted SAMs is characterized by Surface-Enhanced Raman Scattering (SERS) spectra. Bode plots exhibite the capacitance behavior of the imprinted SAMs. Electrochemical cyclic voltammetry sheds some insight on the nature of recognition and isomeric selectivity of the binding sites with respect to different benzenediol isomers. The electrode process for o-hydroquinone is a diffusion-control electrode process. The response of the imprinted SAMs upon target molecules is recorded with capacitance measurements. Faradaic electrochemical impedance studies are consistent with the results of capacitance measurements. Imprinted electrode exhibites isomeric selectivity toward o-hydroquinone among the isomers covering a linear range 2.00×10-7 ~ 1.60 ×10-6 M, with a low detection limit of 2.89×10-8 M. 3. Salicylic acid is used as template to induce the collection of TiO2 particles during the sol-gel process, and recognition sites will form in the inorganic material after salicylic acids are removed by ammonia. Compared with the results obtained on bare and control electrode, selectivity to salicylic acid on the imprinted electrode is greatly improved. Stable responses can be achieved within 10 min covering a linear range from 5.00 × 10-6 ~ 1.50 × 10-4 M, with a detection limit of 3.74 × 10-7 M. The electrode process for salicylic acid is a surface control process. 4. A thin film of imprinted TiO2 is made by surface sol-gel technology, using the interaction between the two hydroxy groups of ascorbic acid molecule and titanium (Ⅳ). Ascorbic acid can been washed from the imprinted film by ammonia and double distilled water respectively, and then recognition sites are created. The imprinted film shows good selectivity toward ascorbic acid. Stable responses can be achieved within 5 min covering a range from 5.00 × 10-6 ~ 1.50 × 10-4 M, with a detection limit of 3.74 × 10-7 M.