The Studies And Applications Of Several Novel Capacitive Biosensors And The Stripping Voltammetric Analysis Of Complex Samples

The fabrication of the chem/biosensor is one of the most promising and interesting areas in the field of analytical chemistry and biochemistry. Especially, the applications of self-assembled monolayer, molecular imprinted technology and nano-materials are distinguished. In this thesis, two new molecularly imprinted capacitive sensors were developed by combining high selectivity molecularly imprinted technology with high sensitivity capacitive transduction. Two new capacitive immunosensors were fabricated profiting from the biocompatibility of electrochemical deposited nano-gold array and capacitive transduction. A selectively penetrated SAM and a nano-gold array were sequentially modified on the glassy carbon electrode, by sensitive stripping voltammetry, trace copper in the presence of excess level of macromolecules was determinated. The analysis of heavy mental ions in complex environmental and biological samples was explored. The main work of this thesis, which was based on the techniques mentioned above, is summarized as follows: 1. A novel biosensor for glutathion direct detection in human serum was proposed by combination of capacitive transduction and molecularly imprinting technique. A two-step kinetic model was successfully derived to describe the recognition process between analyte and imprint sites by capacitive approach. The prospects of future development of this method include further used for the estimation of kinetic and thermodynamic parameters in the MIP recognition process. 2. A new artificial receptor layer was electrosynthesized on the gold electrode to fabricate a capacitive chemosensor. Based on molecular imprinting technique and capacitive transduction, the sensor was applied for herbicide detection. The MIP-modified electrode was selective to mefenacet among other anilide herbicide, and it is applicable to direct mefenacet sensing. Non-MIP-modified electrodes did not show selective response to mefenacet. MIPs proved to be effective as a molecular-recognition element of a chemosensor based on capacitive transduction of the recognized analyte. The preparation of MIPs is simple and low-cost and applicable to various molecules with different structure. The combination of molecular imprinting technique and capacitive transduction will provide simple, specific, and inexpensive sensing systems. This method can be expected for further applications to other herbicides. 3. The barrier properties and electron transfer of self-assembled thiol derivative monolayer modified electrodes in the presence of different surfactants were quantitatively investigated by seriate electrochemical experiments. It was found that by changing the surface structure of SAMs, different surfactants could regulate the barrier properties and electron-transfer efficiency in different ways. A positively charged surfactant lowers the electrostatic repulsion between the negative redox probes and negatively charged surface groups of the monolayer, enhancing the reversibility of electron transfer by virtue of increasing the redox probe concentration within the electric double-layer region. A neutral surfactant shows no significant effect, while a negative surfactant hinders the access and reaction of a redox probe by an electrostatic repulsion of same-sign charges. The adsorption model between the surfactant and the thiol derivative monolayers and the suggested methods can be further used to study the penetration property of biomembranes. 4. A new antibody immobilization strategy was successfully developed for the fabrication of a label-free capacitive immunosensor. Based on electrodeposition of nanometer-sized bioactive hydroxyapatite, covalently coupled with DS and capacitive transduction, the sensor was applied for human transferrin detection. The fabrication and the specificity of the immunosensor were discussed in detail. Compared with traditional immunoassays, the merit of this approach is that it achieved the real-time monitoring the antibody-antigen interaction and omitted the labeling procedure to simplify the analysis process. The immobilization strategy developed in the present work can be applied for the fabrication of other specific immunosensor. 5. An alumina sol-gel-derived ultrathin film was modified on the gold electrode surface followed by an electrochemical deposited nano-gold array. Anti-human transferrin was further immobilized on the nano-gold array to fabricate a novel capacitive immunosensor. 6. A sensitive and convenient voltammetric approach was developed for trace copper determination free from macromolecule interferences using a doublymodified GCE. After successively modified with a direct electrochemically deposited Au nanocrystals array and a spontaneously adsorbed MES monolayer film, the resulting GCE achieved a high sensitivity and a large linear response range in the determination of trace copper, even the concentration of coexisting model contaminants (Tween 80 and BSA) reached 500 ppm. Satisfied results were obtained in the detection of copper in the metallurgic wastewater sample. 7. A sensitive and convenient voltammetric approach was developed for trace copper (II) determination freeing from macromolecular interferences at PMBI film/Au nanocrystals modified GCEs. After successively modified with a electrodeposited Au nanocrystals array and a porous PMBI film, the resulting GCE achieved a high sensitivity and a large linear response range in the determination of trace copper, even the concentration of coexisting model contaminants (BSA and Tween 80) reached 500 ppm. The described method provided an alternative choice for the determination of trace copper in the analysis of complex environmental and biological samples by stripping voltammetry.