| Research Abstract |
Electrochemical sensors for rapid and simple detection of proteins in biological and food samples are desirable. In this study, we have developed a direct protein sensor, which detects proteins as the current signal for their transfer at the oil/water interface. As the fundamental study, we have investigated the voltammetric behaviors of several proteins at the polarized oil/water interface in the presence of anionic surfactants. When the water phase was neutral (pH 7), it was confirmed that reverse micelles formed at the interface could transport proteins into the oil phase. Under these conditions, however, we could not observe any voltammetric wave due to the transfer of proteins other than a small protein, i.e. protamine. When the water phase was acidic (e.g., pH 3.5), however, all the proteins studied gave a well-developed voltammetric wave. Then, the reaction mechanism has been studied in detail, with the help of controlled potential electrolysis. It has been found that under the acidic conditions, protein-containing reverse micelles do not stably exist in the oil phase, and in turn the protein-surfactant complexes are adsorbed at the oil/water interface, giving the voltammetric wave. When the surfactant concentration is high enough, the peak current of the voltammetric wave should be proportional to the protein concentration. The potential, where the voltammetric wave appears, is different between proteins. It has thus been confirmed that the present electrochemical reaction enables us to carry out quantitative and qualitative analyses of proteins and to establish the principle of a new, direct protein sensor. Furthermore, we have made a prototype of an on-line protein sensor using a whole electrolytic cell with a polarized oil/water interface and have examined the basic performance.
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