The fundamental detection scheme of typical grating or photonic crystal (PhC) sensors relies on the correlation of the diffraction behaviors with the refractive index of target analyte. For biomaterial detection, a thin gold film is usually deposited on the sensor surface so that cross linkers can be anchored before functionalizing the device. The nanoscale metallic film suggests plasmonic resonances play a critical role in light-matter interaction. In this work, we demonstrated a compact two-dimensional (2D) hexagonal PhC biosensor with thin gold film coating. In such a device, surface plasmon polariton (SPP) on the metal structure and phase matching of optical wave with the PhC are considered when analyzing light-biomaterial interaction on the detector. Using Epstein-Barr nuclear antigen-1 (EBNA-1) antibody as an example, protein sensing along different lattice orientations of the PhC biosensor was investigated. Based on the dispersion relationship and phase matching conditions, we unravel the mechanisms involved in the wavelength shifts and sensitivities. The simulation results verify the phenomenon of tighter spatial confinement and higher local field intensity from the SPP, which helps detecting small variations of the refractive index on the sensor surface.
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