Abstract
Since localized surface plasmon (LSP) is capable of generating strong electromagnetic fields, it has achieved extensive applications in surface-enhanced Raman scattering (SERS). As opposed to this, surface plasmon polariton (SPP) has been rarely employed for its weak electric field enhancement. The present study proposed an Ag nanoparticles (AgNPs) and multilayer Au/Al2O3 film (MLF) hybrid system, acting as an efficient SERS substrate by coupling LSPs and SPPs resonances. The dispersion relationship indicates that the light scattered by the AgNPs excites the SPP in the MLF, while the electric field is bound to the Au/Al2O3 interface and is significantly enhanced. As revealed from the simulated results, SPPs were generated in the MLF and then coupled with each other to generate a bulk plasmon polariton (BPP). As impacted by BPP, the electric fields stimulated by LSP displayed a dramatic increase. Besides, the electric field exhibited increased intensity with the layer of film. As rhodamine 6G (R6G) and malachite green (MG) were employed as the probe molecules, the AgNPs/MLF hybrid structure demonstrated highly sensitive SERS performance, complying with the theoretical simulations. Specific to the mentioned SERS substrate, R6G and MG had the limit of detection of 1.2 × 10−10M and 7.9 × 10−9M, respectively, demonstrating the prominent prospects of the NPs/MLF hybrid structure in SERS.
Highlights
Surface-enhanced Raman scattering (SERS), for its high sensitivity and specificity in molecular detection, has achieved extensive applications in biosensors, medical diagnostics, and other fields since its discovery on roughened Ag electrodes in 1974.1–5 It has been reported that through the collective oscillation of conduction electrons in metal nanoparticles (NPs), i.e., localized surface plasmon (LSP), a strong electromagnetic field can be generated on the metal surface
As revealed from the results of both simulation and experiment, the electric fields among the topmost Ag nanoparticles (AgNPs) displayed a noticeable improvement by the multilayer Au/Al2O3 film (MLF)
It is noteworthy that the Au/Al2O3 film layer could be stacked to lead to the production of stronger electric fields
Summary
Surface-enhanced Raman scattering (SERS), for its high sensitivity and specificity in molecular detection, has achieved extensive applications in biosensors, medical diagnostics, and other fields since its discovery on roughened Ag electrodes in 1974.1–5 It has been reported that through the collective oscillation of conduction electrons in metal nanoparticles (NPs), i.e., localized surface plasmon (LSP), a strong electromagnetic field can be generated on the metal surface. When the gap between adjacent NPs reaches the order of tens of nanometers, the LSPs generated by the NPs can be coupled to each other to elevate the electromagnetic fields, and the Raman intensity can be 2–4 orders of magnitude stronger than that of a single nanoparticle.. To increase the hot spot density more significantly, Lin et al proposed a three-dimensional (3D) SERS substrate composed of multilayer Ag nanocubes.. To increase the hot spot density more significantly, Lin et al proposed a three-dimensional (3D) SERS substrate composed of multilayer Ag nanocubes.15 By drawing upon such a 3D structure, hot spots are generated between adjacent NPs both horizontally and vertically, which can be coupled with each other to generate stronger hot spots at the topmost layer.
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