Impact of Fabrication and Bioassay Surface Roughness on the Performance of Label-Free Resonant Biosensors Based On One-Dimensional Photonic Crystal Microcavities

Micro- and nanofabrication offer remarkable opportuniies for the preparation of label-free biosensors exploiting optical resonances to improve sensitivity and reduce detection limit once specificity is imparted through surface biofunctionalization Nonetheless, both surface roughness, peculiar of fabrication processes, and bioassay roughness, resulting from uneven molecular coverage of the sensing surfaces produce light scattering and, in turn, deterioration of biosensing capabilities, especially in resonant cavities where light travels forth and back thousands to million times. Here, we present a quantitative theoretical analysis about the impact of fabrication and bioassay surface roughness on the performance of optical biosensors exploiting silicon-based, vertical one-dimensional (1D) photonic crystal resonant cavities, also taking noise sources into account. One-dimensional photonic crystal resonant cavities with different architectures and quality factors ranging from 10(2) to 10(6) are considered. The analysis points out that whereas sensitivity and linearity of the biosensors are not affected by the roughness level either due to fabrication or bioassay, the limit of detection can be significantly degraded by both of them, depending lon the quality factor of the cavity and noise level of the measurement system. The paper provides important insights into performance versus design, fabrication, and readout of biosensors based on resonant ID photonic crystal cavities for real-setting operation.