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

Abstract

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.

Whispering gallery mode sensors

“…Examples of receptor molecules that have been used and studied in WGM biosensing applications include oligonucleotides, which bind (hybridize) sequence-specifically to single-stranded nucleic acids [4,277–281]. Other examples include antibodies, which are widely used for detecting proteins [282–286] and aptamers [285,287]. A particular challenge when working with antibodies lies in finding a functionalization protocol that attaches the antibodies to the sensor surface without impeding their specific binding capabilities, maintaining their preferred orientation, etc.…”