| Summary: | 博士 === 臺灣大學 === 化學工程學研究所 === 98 === This dissertation deals with chemically modified electrodes and molecularly imprinted polymer (MIP) electrodes for electrochemical biosensors. The electrochemical biosensors were based on modifying mediators and MIP. Initially, a novel amine-imide type conducting polymer, denoted as poly(PD-BCD), was molecularly imprinted with uric acid (UA). The results revealed that the imprinting efficiency (IE) was highly associated with the polymer content. It was found that the optimum polymer content at 0.6 wt% gives the highest imprinting efficiency of 3.73. The sensitivities of the MIP and the non-MIP (NMIP) electrodes made with 0.6 wt% of polymer were calculated to be 24.72 and 6.63 μA/ mM cm2, respectively. The limit of detection (LOD) for the MIP electrode was found to be 0.3 μM. This MIP electrode was used as a biosensor for the detection of UA in the presence of ascorbic acid (AA) in a sample containing these species in the same concentrations as those in a human serum. Only 7% increase in current was noticed when sensing the mixed sample, as compared to the UA sample alone. In further research, a non-conducting polymer, poly-methacrylic acid (PMAA) was polymerized on the surface of multi-walled carbon nanotubes (MWCNTs) for sensing UA. The adsorption isotherms suggest that a good IE of 4.41 for UA. The adsorption isotherms were correlated successfully by the Freundlich model. Amperometric detection also revealed similar aspect, as compared to the adsorption data, and showed high selectivity toward AA, with an IE value of 2.05. For the extension of non-conducting polymers, a novel MIP electrode was fabricated by using a mediator as the reactive center and a MIP layer as the recognition part. Because of this new system, reactive mediators were investigated subsequently.
It was found that quercetin (Q), an ideal mediator, possesses catalytic effect to the neurotransmitter which was named dopamine (DA). Glassy carbon (GC) electrode was modified using MWCNTs, quercetin and Nafion® in this sequence. A possible reaction mechanism between Q and DA was proposed. The amperometric detection potential was fixed at 0.45 V (vs. Ag/AgCl sat’d KCl) as determined by the linear sweep voltammetry (LSV). The GC/MWCNTs/Q/Nafion® electrode shows a current density of about 900 µA cm-2 for DA, comparing to that of 80 µA cm-2 for the GC electrode. The 11-fold sensitivity enhancement for the modified GC electrode in sensing DA is attributed to the composite modification of the electrode. The composite electrode does eliminate the interference against AA. Calibration curves of batch and flow systems were obtained by amperometry for the detection of DA. Moreover, another mediator, flavin adenine dinucleotide (FAD), which plays a role of reducing agent for hydrogen peroxide (H2O2), was found. FAD was immobilized on a poly(3,4-ethylenedioxy-thiophene) (PEDOT) conducting polymer-modified GC electrode and was proposed to detect H2O2. The amperometric detection potential was fixed at -0.40 V (vs. Ag/AgCl sat’d KCl) as determined by the LSV. The sensitivity and the LOD for the GC/PEDOT-FAD electrode were 92.3 mA/M cm2 and 143
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