Abstract
We designed and fabricated guided-mode resonance (GMR) gratings on indium-tin-oxide (ITO) thin film to generate a significantly enhanced local electric field for surface-enhanced Raman scattering (SERS) spectroscopy. Ag nanoparticles (NPs) were self-assembled onto the surface of the grating, which can provide a large amount of “hot-spots” for SERS sensing. The ITO gratings also exhibit excellent tolerance to fabrication deviations due to the large refractive index contrast of the ITO grating. Quantitative experimental results of 5,5’-dithiobis(2-nitrobenzoic acid) (DTNB) demonstrate the best enhancement factor of ~14× on ITO gratings when compared with Ag NPs on a flat ITO film, and the limit of detection (LOD) of DTNB is as low as 10 pM.
Highlights
Surface-enhanced Raman scattering (SERS) is a powerful technique that can provide ultra-sensitive and non-destructive characterization of various kinds of molecules [1]
We used DiffractMod module in RSoft, which is based on rigorous couple wave analysis (RCWA), to design the ITO gratings
The guided-mode resonance (GMR) of the ITO grating is formed by the optical coupling between the discrete guided modes of the photonic crystal slab and the radiation continuum above the light line
Summary
Surface-enhanced Raman scattering (SERS) is a powerful technique that can provide ultra-sensitive and non-destructive characterization of various kinds of molecules [1]. We demonstrated SERS sensing using bio-enabled photonic crystal structures, in which a monolayer of Ag NPs were self-assembled on diatom frustules [16,17] In these studies, the LSPs of Ag NPs was coupled with the GMRs of diatom frustules, which provided stable SERS enhancement in addition to the existing SERS effect of Ag NPs. due to the variation of the shape and dimension of the naturally-obtained diatom frustules, the SERS enhancement of diatom-based substrates is not as high as rationally designed gratings. The essential idea towards high sensitivity SERS detection is the engineering of the GMR grating, which can produce a universal increase of the SERS signal intensity across the entire substrate with a high density of hot-spots. SERS substrates demonstrate significant Raman enhancement capability, and the quantitative SERS characterization of DTNB on gratings showed that the LOD of the ITO gratings is 10 pM
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