Development of precise visualization system for small transient diffusion field of protein using phase shifting interferometer

This paper deals with a development of precise visualization system for mass diffusion field of micro quantity proteins by using phase shifting interferometer. The visualization system developed in this study could solve several measurement difficulties and accomplish quick and precise measurement of mass diffusion coefficient. For the observation of small transient diffusion field, Mach-Zehnder type phase shifting interferometer and small shearing cell were utilized. The designed small shearing cell requires only 10 micro liter solutions to form the transient diffusion field. As a target protein, lysozyme extracted from hen egg white was used. For the avoidance of protein denaturation, the lysozyme was dissolved in universal buffer solution over a wide pH range from pH 4.29 to 8.44. This range corresponds to that of digestive system in human body. Also, to investigate concentration dependency of mass diffusion coefficient, solutions over a wide range of concentration were prepared. The experimental results indicated that the concentration profile in a diffusion field could be detected clearly even though the field of view is smaller than 1.0mm square. The mass diffusion coefficient was derived by an analytical method proposed by authors. This method can derive mass diffusion coefficient as a function of concentration from one measurement datum. From the experimental data, the dependency of pH value of surrounding buffer and that of concentration on diffusion phenomena were discussed.