Optimum grating parameter for diffractive label-free biosensing

Abstract

A modified functionalized diffraction grating can act as a biosensor that can convert biorecognition events into analyzable signals. By detecting the changes in the intensity of the first order diffraction efficiency, the biosensor can detect the adhesion of target molecules on the grating surface. We want to determine the optimal grating parameters such that the first order diffraction of the grating will change rapidly with the adhesion of analytes. Using scalar diffraction theory, we can derive an analytical expression for the diffraction efficiency and find the optimal groove height and phase difference of a grating. The optimal height is λ/2, making the optimal phase difference π/2. We also want to analyze the effects of surface roughness on the diffraction efficiency by simulating a rough diffraction grating. The surface roughness reduces the resulting overall intensity and diffraction efficiency as the rough surface causes light to be scattered randomly. Furthermore, as the surface becomes rougher, the harder it is for the grating to indicate whether the changes in the first order is from analyte adhesion and not the surface roughness.