JPhys Photonics (Jan 2024)
Hybrid modes in multilayer/antenna architecture set side-band-selective molecular Raman scattering
Abstract
Technologies with tag- less capacity for analyzing molecules, are poised to make significant advancements in the healthcare industry with a substantial potential to improve sensitivity for individual molecules and binding events. Plasmonics has the potential for enhanced system response when emitters are included in the full architecture. Here, a hybrid multilayer including a sequence of metals and dielectrics has been examined. The surface of the multilayer is covered with 30 -μ m height features working as plasmonic antennae. Their contribution to the emission of the system has been analyzed. The multilayer has been coupled with a prism to excite the polaritons in an experimental optical setup to measure the reflected and transmitted signals. The measurements demonstrate the surface plasmon polariton/antenna mode hybridization. The optomechanics of the plasmonic resonant multilayer has been studied with reference to the refractive index of the surrounding medium as well as to the incident angle of the exciting beam. Then, the experimental shifts have been measured according to the optomechanical spectrum of the naïve plasmon resonant multilayer. The optomechanics of the plasmonic resonant multilayer, which has shown a natural resonance at $\omega = 96 \,\text{MHz}$ , has been coupled with a molecular emitter, e.g. a dye. As the concentration of the red dye increases, the intensity of the peaks at $\omega \gt 96 \,\text{MHz}$ raises, suggesting an important sensitivity in the anti-Stokes domain. On the other side, the decay is equal to $\kappa = 1.1\times10^{-2} \,\text{MHz}$ showcasing a high quality factor ( $Q = 9.6\times10^{3}$ ). For validation of increased sensitivity in the anti-Stokes region, bovine serum albumin (BSA), a protein active in the Raman region, has been tested and, through an image-based analysis, the molecular pattern recorded. The demonstrated potential of utilizing optical resonance shifts to investigate molecular patterns is highly promising. Therefore, the proposed sensing method represents a significant advancement in the field, offering new opportunities for the sensitive detection of biomolecules.
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