High-Resolved Near-Field Sensing by Means of Dielectric Grating With a Box-Like Resonance Shape

In the last ten years, advances in diagnosis and treatment have played a significant role in counteracting the growth of dangerous diseases. Recently, several studies have demonstrated that monitoring proteins in the human body helps predictive monitoring of human health conditions and disease progress. In this context, bio-recognition techniques with high resolution are crucial. Evanescent-field biosensors have been widely investigated and successfully developed thanks to their ultrahigh sensitivity. However, their resolution is mitigated by the nature of the Lorentzian spectral line shape that shows inevitable significant spectral overlap among similar concentration-related resonances. To overcome this problem, a novel ultra-compact photonic biosensor with a tailored resonance shape is proposed. The device consists of 1-D photonic crystal (PhC) with engineered defects to achieve resonance with a box-like shape, a very large roll-off (=−10.50 dB/oct.), within a small footprint ( $\approx {1}\cdot {10}^{-{2}}\,\,\mu \text{m}^{{2}}$ ), enabling single wavelength interrogation. The strong biosensor–analyte interaction is associated with a larger transmission change with respect to biosensors with Lorentzian shape (> 4 versus > 0.5 dB for proteins Immunoglobulin-G (IgG) concentration from 1 to 500 pg/mL), drastically decreasing the read errors.