Theoretical Design of an Integrated Optical Sensor for a Standard Immunoassay

Immunoassay is a biochemical test that measures the presence or concentration of biomolecule in a solution by the means of the antibody (or antigen). Most immunoassays involve chemically linking antibodies or antigens with some kind of detectable labels which produce measurable signals in response to the binding. The use of labels creates problems, including complexity in the screening process and probable influence on the nature of target molecular. To overcome the drawbacks, we theoretically demonstrate an integrated Mach-Zehnder interferometer (MZI) with n-shaped slot waveguide based on finite-element method. Dual polarization can be strongly confined in the slot where the analytes are accommodated. The interaction between the optical field and tested solution is greatly enhanced, resulting in high sensitivity of the device. The detection of surface adsorbed molecule densities is down to 0.176pg/mm
²
for transverse electric mode and 1.27pg/mm
²
for transverse magnetic mode. The integrated MZI with identical configuration of both arms make the parallel-control trial available thereby effectively preventing the unspecific binding and background from biological materials. Wavelength interrogation was taken to monitor the antibody-antigen recognition.