Development of planar waveguide-based immunosensor for detection of low molecular weight molecules such as mycotoxins

A biosensor experimental set-up based on a silicon oxide/silicon nitride/silicon oxide waveguide operating as polarization interferometer was designed, built, and tested. The operation principle of the proposed sensor lies in the detection of a phase shift between p-and s-components of polarized light. The mode of operation of the proposed sensor is similar to that of Mach-Zehnder interferometer, while its design is much simpler and does not require splitting the waveguide into two arms. The refractive index sensitivity of the polarization interferometer sensor in the range of 1200 radians per refractive index unity (RIU) was evaluated. Several biosensing tests were conducted on detection of aflatoxin B1 in direct immunoassay with specific antibodies immobilized in the sensing window. Binding of 0.01 ng/ml (10 ppt) of aflatoxin B1 appeared to cause a phase shift of approximately one period. This is a remarkably high sensitivity (especially for direct immunoassay format) which the detection of mycotoxins in much lower concentrations in ppt level. (C) 2017 Published by Elsevier B.V.