Optical constant measurement of GOx thin film with circular heterodyne interferometry

Glucose oxidase (GOx) is widely used in optical biosensors for glucose concentration measurement. There is relatively little information about the refractive index (RI) and thickness of GOx thin film at different pH levels. This study develops a precision circular heterodyne interferometer to measure RI and thickness of GOx immobilized on the glass substrate. The results of this study reveal the non-linear dependence of RI on the pH levels of GOx, but the thickness is independent on pH levels of GOx. In addition, the comparison results are provided by commercial ellipsometer for measuring both RI and thickness and there is no significant difference between proposed method and comparison methods.