Broadband Long-Wave Infrared On-Chip Silicon-based Surface-Enhanced Laser Spectroscopy Enabled by Gradient Nanoantenna Array

Silicon-based on-chip broadband surface-enhanced infrared absorption (SEIRA) is highly desired for integrated micromolecular detection systems, taking advantages of CMOS mass production, low cost, high sensitivity, etc. However, the silicon platform is difficult to operate in the mid-infrared wavelength region above 4 µm where abundant fingerprint characteristics of biomolecules are located, because of the strong absorptions in silicon dioxide cladding above 4 µm. Here, a large-core rib silicon waveguide-integrated gradient nanoantenna array is proposed for broadband long-wave infrared biomolecular detection. It is shown that Low loss propagation of light in the long-wave infrared region up to 7 µm (1428 cm⁻¹) in silicon photonics can be achieved while avoiding complex fabrication techniques. A gradient nanoantenna array is designed on the waveguide to achieve broadband enhancement from 5 to 7 µm (1428–2000 cm⁻¹). Laser spectroscopy of bovine serum albumin on the chip is demonstrated, showing enhancement of absorbance by approximately ten times over laser transmission spectroscopy in the amide bands. Such a platform opens up a new horizon of silicon-based on-chip SEIRA biomolecular detection.