Analytical Sciences

Optical Characterization of the Antigen–Antibody Thin Layer Using the Whispering Gallery Mode

Takeshi TAJIRI,*,** Shuzo MATSUMOTO,* Toshihiko IMATO,*** Toshihiro OKAMOTO,** and Masanobu HARAGUCHI**

*Industrial Technology Center of Nagasaki, 2-1303-8 Ikeda, Omura, Nagasaki 856-0026, Japan
**Department of Optical Science and Technology, Faculty of Engineering, The University of Tokushima, 2-1 Minamijosanjima, Tokushima 770-8506, Japan
***Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, 744 Moto-oka, Nishi, Fukuoka 819-0395, Japan

We immobilized an antibody (anti-β-Galactosidase) on a polystyrene microsphere by using a covalent bond, and observed the resonance peaks in the scattered light intensity spectra related to the whispering gallery mode (WGM) excitation of the microsphere. The amount and the optical parameters, i.e., thickness and refractive index, of anti-β-Galactosidase on the sphere surface were evaluated based on an absorbance measurement and a resonance peak shift measurement, respectively. Moreover, we measured the variation of the WGM spectra depending on the concentration of the enzyme solution (β-Galactosidase), which allowed us to optically evaluate the thickness and the refractive index of the antigen–antibody layer from the shift of the WGM spectra peak.

J-STAGE: View this article in J-STAGE