Abstract
A hybrid integration of nanoplasmonic antennas with silicon nitride waveguides enables miniaturized chips for surface-enhanced Raman spectroscopy at visible and near-infrared wavelengths. This integration can result in high-throughput SERS assays on low sampling volumes. However, current fabrication methods are complex and rely on electron-beam lithography, thereby obstructing the full use of an integrated photonics platform. Here, we demonstrate the electron-beam-free fabrication of gold nanotriangles on deep-UV patterned silicon nitride waveguides using nanosphere lithography. The localized surface-plasmon resonance of these nanotriangles is optimized for Raman excitation at 785 nm, resulting in a SERS substrate enhancement factor of 2.5 × 105. Furthermore, the SERS signal excited and collected through the waveguide is as strong as the free-space excited and collected signal through a high NA objective.
Highlights
Silicon photonics based on high index-contrast silicon-on-insulator (SOI) waveguides has proven to be an excellent platform for biosensing
The absorption spectrum of this nanopattern is well suited for Raman spectroscopy in the near-infrared, a wavelength region interesting because of its low absorption by biological specimen, reasonably strong scattering and low background fluorescence
Surface-enhanced Raman scattering (SERS) data show that the SSEF of this pattern is 2.5 × 105, and that excitation and collection of SERS spectra through the waveguide is at least as efficient as using the best possible air objective
Summary
Silicon photonics based on high index-contrast silicon-on-insulator (SOI) waveguides has proven to be an excellent platform for biosensing. The success of the SOI platform is largely due to the use of standard CMOS-fabrication techniques, which ensures high-volume manufacturing, reproducible components and potential CMOS compatibility This inspired the development of a silicon nitride (SiN) counterpart, paving the way for deep-UV fabricated integrated photonics at visible wavelengths. Recent efforts succeeded in combining plasmonic antennas with Si [15] and SiN [16,17,18] waveguides, providing proof-of-concept experiments for integrated localized surface plasmon resonance (LSPR) sensing [18] and even waveguide-excited and -collected SERS [17] All these approaches rely on multiple electron-beam lithography steps with critical alignment for writing both the waveguides and the nano-antennas. To the best of our knowledge, this is the first demonstration of an e-beam free platform for on-chip SERS, an important step towards a complete on-chip SERS-platform combining the sensing area, filters, spectrometer and even the laser on a single chip
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