FDTD simulation of a graphene-coated multilayer waveguide antibody biosensor for infection and vaccine-induced immunity assessment

A compact hybrid-plasmonic biosensor was numerically investigated (3D FDTD) to evaluate the immune response to COVID-19. The device uses a 220 nm-wide Si–SiO2–Al–Si waveguide with PtSe2-graphene bioreceptors functionalized with the spike RBD; anti-spike IgM/IgG are detected via a Goos-Hänchen shift from surface-index changes. A sensitivity of 3 W·RIU−1; (+30% vs. prior studies) and a 5.2× increase in effective interaction were obtained, with reduced loss and a propagation length of 42.2 µm. Dispersion remains low across the operating band, and detuning up to 20 GHz is negligible due to the micrometer-scale interaction length. The novelty lies in optimizing the waveguide so that antigen–antibody interaction strength modulates the power or mode area at the output port, enabling simple photodiode readout.