Electrochemical Sensors for Vinyl Chloride and Protein

• Main Authors: Min-Chieh Chuang, 莊旻傑
• Other Authors: Ming-Chang Yang
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/4esuv6

博士 === 國立成功大學 === 化學工程學系碩博士班 === 92 === 　　This thesis is divided into two parts. A development route toward a practical vinyl chloride gas sensor was exploited in the first part. In the beginning stage, a novel sensing configuration consisting of one porous alumina substrate, two electrodes sputtered on separate sides, and an organic electrolyte, was developed to in-situ analyze gaseous vinyl chloride. Gold and platinum electrodes with several solvents, e.g., 1,4-dioxane aqueous solution, acetonitrile, and toluene/DMF mixtures, were applied to investigate the suitability for the analysis of vinyl chloride in the concentration range of 13~44.5%. The best solvent composition, 50% toluene/50% DMF, was employed for the determination of vinyl chloride with concentration range of 0.5-4%. Several variables, including type of supporting electrolyte, applied potential, concentration of supporting electrolyte, and porosity of alumina substrate were investigated to find the highest sensitivity for vinyl chloride, 70.9 �A %-1, obtained at –2.1 V (vs. Ag/Ag+) in 50% toluene/50% DMF electrolyte containing 10 mM Bu4NClO4 supporting electrolyte. However, the interference of moisture from both the electrolyte and the testing gas were significant and diminished the development of this detector toward a low concentration, less than 1000 ppm. 　　For this reason, an indirect sensing method was proposed which employed a pre-pyrolysis column followed by an amperometric sensor. A significant sensing ability to the pyrolyzed gas, produced from a pyrolysis of 0-30 ppm vinyl chloride gas, was obtained with a Pt/porous alumina substrate assembly. The sensing current was proportional to the concentration of vinyl chloride. The sensitivity and sensing limit for vinyl chloride were functions of pyrolysis temperature, gas flow rate, and applied potential. The highest sensitivity of 6.87 �A ppm-1 was obtained under the preferable sensing parameters, 400 �aC, 150 ml min-1 and 1.2 V (vs. Ag/AgCl), in which the sensing reaction was controlled by gas diffusion. Effect of porosity of porous alumina substrate on the sensing performances was also studied. The electroactive species in the pyrolyzed gas for sensing was found to be hydrogen chloride vapor. 　　To overcome the drawback, a long response time, in the indirect sensing mode, an alternative sensing device, based on a NASICON thick-film electrolyte, was developed. Three types of NASICON inks with distinct constituents were prepared for the fabrication of the porous thick-film electrolytes. The physical properties of the porous electrolyte layer, e.g., morphological structure, thickness, adhesion, and XRD spectrum, were studied and found relevant to the composition of the ink. The electrochemical property of the fabricated sensing device with these inks was also investigated. Responding curves of the sensing devices to 20-50 ppm vinyl chloride gas were examined. Effects of electrode material (Pt and Au) and oxygen on the sensing behavior were discussed. Better sensing performances, with a sensitivity of 8.2�b2.2 nA ppm-1 and 250 seconds response time, was obtained on Pt sensing electrode under air atmosphere. 　　In the second part of this thesis, a simple biosensor, based on a tyrosinase-immobilized electrode, was developed for a rapid and quantitative measurement of bovine serum albumin (BSA) and human serum albumin (HSA). Tyrosinase, immobilized on a screen-printed carbon electrode, catalyzed the oxidation of tyrosine residues present in the albumin to the corresponding quinone, which was further reduced electrochemically by the sensing electrode under an appropriate condition. The concentration of protein, therefore, could be quantified by measuring the reduction current. The operational parameters that affect the performance of this biosensor, e.g., working potential, pH, and temperature, were assessed and optimized. The stability, lifetime, reproducibility, and interference of this biosensor were also evaluated. This biosensor indicated that this method was not only a highly sensitive assay for albumin (2523.1 nA�ml�mg-1 for 0.2-0.5 mg ml-1 BSA) but also a potential tool for the measurement of total protein in human serum.