No abstract

The capability to support large wave vector bulk plasmon polariton (BPP) waves enables the application of hyperbolic metamaterials (HMMs) in sensing. However, there is a challenge arising from the excitation of BPP, and the highly confined polarization waves are unable to meet the requirements of practical application. In this study, an HMM/bilayer silver nanoparticles (Ag NPs) platform is proposed that allows the excitation and utilization of BPP for use as a surface-enhanced Raman scattering (SERS) substrate. According to the research results, the bilayer Ag NPs provide stronger plasmonic property and act as a light-matter coupler, so as to generate a large wave vector of scattered light and excite the BPP within the HMM. Besides, Ag NPs provide the nano antenna structure, and decouple the BPP into localized surface plasmon (LSP) that can be used directly to excite the electric fields. In addition, HMM produces a modulating effect on the plasmon resonance peak, which makes it possible to overlap the spectrum of resonance peak with excitation wavelengths, thus leading to a strong absorption peak at the incident laser wavelength region. Experimentally, the platform was applied to achieve SERS detection for adenosine molecules with a concentration of 10−6 M. It is believed that this plasmonic platform has a potential of application in surface-enhanced spectroscopy.

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.

In the present study, an optical fiber surface plasmon resonance (SPR) biosensor was developed for measuring time- and concentration-dependent DNA hybridization kinetics. Its design complies with a 3D Au / Al 2 O 3 multilayer composite hyperbolic metamaterial (HMM), a graphene film, and a D-shaped plastic optical fiber. According to the numerical simulation and the experimental demonstration, the SPR peak of the designed biosensor can be effectively altered in the range of visible to near-infrared by varying the HMM structure. The sensitivity of the appliance was shown to achieve a value of up to 4461 nm/RIU, allowing its applicability for bulk refractive index sensing. Furthermore, a biosensor designed in this work displayed high-resolution capability (ranging from 10 pM to 100 nM), good linearity, and high repeatability along with a detection limit down to 10 pM, thus suggesting a vast potential for medical diagnostics and clinical applications.

In the present study, a nanoparticle-multilayer metal film substrate was presented with silver nanoparticles (Ag NPs) assembled on a multilayer gold (Au) film by employing alumina (Al2O3) as a spacer. The SERS performance of the proposed structures was determined. It was suggested that the SERS effect was improved with the increase in the number of layers, which was saturated at four layers. The SERS performance of the structures resulted from the mutual coupling of multiple plasmon modes [localized surface plasmons (LSPs), surface plasmon polaritons (SPPs), as well as bulk plasmon polaritons (BPPs)] generated by the Ag NP-multilayer Au film structure. Furthermore, the electric field distribution of the hybrid system was studied with COMSOL Multiphysics software, which changed in almost consistency with the experimentally achieved results. For this substrate, the limit of detection (LOD) was down to 10−13 M for the rhodamine 6G (R6G), and the proposed SERS substrate was exhibited prominently quantitatively detected capability and high reproducibility. Moreover, a highly sensitive detection was conducted on toluidine blue (TB) molecules. As revealed from the present study, the Ag NP-multilayer Au film structure can act as a dependable SERS substrate for its sensitive molecular sensing applications in the medical field.