Spectroscopic Ellipsometry Based Biosensor on Gold Thin Film for Detection of Microalgae

Abstract

The study of spectroscopic ellipsometry on gold thin film with different thicknesses (30, 50, and 70 nm) for biosensor application has been done. In this work, a rotating analyzer ellipsometer (RAE) has been used to characterize gold thin film and detect microalgae. The measurement was performed at different incidence angles (60°, 65°, 70°, and 75°) assuming the gold film as an isotropic material. The light absorptions of electron represented by the ellipsometer parameter (Δ) and the extinction coefficient (k) are due to the intraband transition of free electrons in the lower photon energy and interband transition of bounded electrons from 5d to 6sp in the higher photon energy. The light absorption increases with the decrease in the thickness of Au thin film. However, for the detection of microalgae, the light absorption of the electron increases with the increase in the thickness of Au thin film due to the dominant absorption by microalgae and PVA. We report that the use of Au thin film with the thickness of 70 nm provides the most sensitive detection of microalgae which is confirmed by the change in Δ (63.1°), at the photon energy of 2.11 eV and the incidence angle of 75°.