STUDY OF ELECTROCHEMICAL POLYMERIZATION OF THIOPENE AND THIOPHENE-3-ACETIC ACID AND THEIR APPLICATIONS AS CHEMICAL PROBES FOR ANALYSIS

Abstract

A new glucose sensor was fabricated by the use of microemulsion polymerization of thiophene. The oil-in-water microemulsion was a simple 3-component system consisting of a non-ionic surfactant, monomer thiophene and an aqueous buffer, without the use of organic solvent. Enzyme was entrapped by the deposition of a thin layer of non-conducting polythiophene. This enzyme layer could be restored readily by the same microemulsion polymerization procedure, when the enzyme was depleted. Application of this glucose sensor system in a flow-cell electrode was performed successfully. A linear range over three orders of magnitude of glucose concentrations and a detection limit of nanomole level were readily achieved. The capability of this new technique has been demonstrated in connection with a high performance liquid chromatography for the direct sensing of glucose in a fresh orange In the second part of this work, a new method for preparing charge-selective polythiophene and poly(thiophene-3-acetic acid) films was described. The polymers were coated onto a micro flow-cell electrode using constant current electropolymerization. These polymer-modified electrodes exhibited charge-selective responses towards ascorbic acid, catechol and dopamine, when polymerized from solutions containing optimum amounts of water Investigations by infrared and X-ray photoelectron spectroscopies showed that electron-rich oxidized carbon groups were responsible for polythiophene's charge-selective property Whereas, poly(thiophene-3-acetic acid) is inherently charge-selective, and its charge-selective property was observed only when film porosity or the film was increased by the impeding effect of water on polymer growth during polymerization In the final part, these charge-selective polymer-modified electrodes derived from poly(thiophene-3-acetic acid) were applied in the detection of other charged analytes which included neurochemicals such as L-DOPA, methyldopamine, (±)- norepinephrine and (±)-epinephrine. It was found that poly(thiophene-3-acetic acid) modified electrode prepared under waterless condition possesses size-selective property. This newly discovered property of poly(thiophene-3-acetic acid) was applied in a glucose sensor, which exhibited high selectivity for glucose and effectively exclude interferents such as ascorbic acid and uric acid.