Construction Of Novel Molecularly Imprinted Electrochemical Sensors And Investigation On Direct Electrochemistry Of Protein

Molecularly imprinted polymers (MIPs) are becoming an important class of synthetic materials mimicking molecular recognition by natural receptors. The general principle of molecular imprinting is based on such a process where functional and cross-linking monomers are copolymerized in the presence of a target analyte which acts as a template. Upon removal of the molecular template, the material retains its moulded shape to fit and coincide with that of the template molecules. Thus, MIPs can selectively bind to molecules of interest. 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, slow mass and charge transfer, high detection limit, bad reversibility and reproducibility, etc.To overcome some of the difficulties associated with traditional MIPs matrices, three new electrochemical sensors are constructed successfully in the thesis by coupling electropolymerization, sol-gel process and self-assembled monolayers (SAMs) with molecular imprinting technology, using porous gold film and multiwalled carbon nanotubes (MWNTs) to amplify the response signal.In addition, the direct electron transfer between redox proteins and electrode surface are of great importance for not only studying the electron transfer between biomolecules in biological system, but also investigating the novel enzyme biosensors. A novel composite material was used to investigate the direct electrochemistry of hemoglobin in this thesis.The main points of this thesis are summarized as follows:1. A new electrosynthesized polydopamine (PDA) imprinted film that can be used as the recognition element in the capacitive sensing of nicotine has been successfully developed. Cyclic voltammety (CV) and electrochemical impedance spectroscope (EIS) were used to investigate the capacitive performance of the PDA imprinted film. A real-time detection of nicotine was carried out using impedance-time method. Stable responses can be achieved within 10 min covering a linear range from 1.0×10^-6～2.5×10^-5 M, with a low detection limit of 5.0×10^-7 M.2. An amplified self-assembled molecular imprinted monolayer for L-serine recognition on electrodeposited porous gold film was developed. L-cysteine was chosen as assembling monomer and L-serine was used as template. Porous gold film can effectively increased the recognition sites for template molecule in imprinting process. Stable response is achieved within 5 min, covering a linear range from 5.0×10^-6～2.0×10^-4 M, with a sensitivity of 215 mA M^-1, and a detection limit of 4.8×10^-7 M. The analytical performance of imprinted sensor proposed is more sensitive compared to the imprinted sensor without porous gold film modified. 3. A new type of dopamine imprinted sensor based on multi-walled carbon nanotubes (MWNTs) and silica sol-gel composite material was developed. The sol-gel film was used to imprinting dopamine on the surface of glassy carbon electrode (GCE). MWCNTs were used to increase the current response. Analytical characteristics of the sensors with and without MWNTs were compared, and the results showed that analytical performance of the sensor could be improved greatly after introduction of the MWNTs. Stable response is achieved within 5 min, covering a linear range from 1.0×10^-7～2.0×10^-4 M, with a detection limit of 3.7×10^-8 M. 4. CNTs have been used to investigate the direct electrochemistry of protein extensively, mostly, the surface functionalization of CNTs were achieved under strong oxidizing conditions for the introduction of carboxylic acid groups, however, this treatment may introduce defects to the pristine CNTs and thus compromise the electronic and mechanical properties which is undesirable. A novel composite material of non-destroyable surface decoration of pristine CNTs with chitosan (CHIT-MWNTs) was applied to investigate the direct electrochemistry of hemoglobin (Hb). Hemoglobin was entrapping in CHIT-MWNTs nanocomposite, the direct electron transfer of Hb and catalysis toward hydrogen peroxide (H₂O₂) were invesitaged in this thesis. CHIT-MWNTs nanocomposite can form a three-dimensional network film and provide a suitable biomembrane-like microenvironment for Hb, which greatly facilitated the electron transfer between Hb and electrodes. The biosensor exhibited a wide linear response range of 1.0×10^-6～1.5×10^-3 M with a detection limit of 5.0×10^-7 M. for the detection of H₂O₂.