Microscale Resonator Antenna Array Design on a Silica-Aerogel Substrate for Surface-Enhanced Raman Scattering in the Detection of Diluted Furfural.

To augment the feeble Raman scattering signal using a surface-enhanced Raman scattering (SERS) substrate, the directivity and reflection of the generated signal are critical factors. The heating impact of nano-SERS on silicon wafers, induced by strong laser power excitation, frequently leads to an elevation in the Raman spectrum profile, rendering certain changes with minimal intensity undetected. We proposed and demonstrated that the microscale resonator array of the dipole antenna architecture on Si-aerogel considerably amplified the Raman shift intensity of furfural. The microscale SERS chip consists of three material layers: a resonator antenna array layer (quartet-split silver rings), a dielectric material layer (Si-aerogel), and a ground layer (thin silver coating). The optimal dimensions of the quartet-split silver rings were determined through electromagnetic field simulation to ensure that excitation of the microscale SERS chip by a 785 nm (381 THz) laser induces localized surface plasmon resonance (LSPR) at the interface between the resonator antenna array layer and the dielectric material layer, thereby producing a strong localized electromagnetic field (EM) directed toward the numerical aperture of the microscope Raman spectrometer. The microscale resonator antenna array amplifies the Raman Stokes intensity at low concentrations of furfural owing to its elevated reflection coefficient throughout the whole Raman shift bandwidth. The hydrophobic absorbent property and low thermal conductivity of the monolith Si-aerogel markedly improve the detection of highly diluted furfural in aqueous solutions by drawing analytes toward the electric field hotspot of the SERS chip. In contrast to nano silver thin film-SERS, each Raman shift bandwidth of furfural can be clearly identified without spectral interference from xylitol. The microscale Si-aerogel SERS device generates a measurable Raman signal with an analytical enhancement factor (AEF) of up to 584, contingent upon the shift number, in comparison to an optical mirror.