We proposed a high sensitivity and a high resolution surface plasmon resonance sensor composed of graphene–WS₂ hybrid nanostructure and Au–Ag bimetallic-layers film.

Electrically modulated surface enhanced Raman scattering (E-SERS) can be able to regulate the plasmon resonance peak of metal nanostructures, further improve the detection sensitivity of the SERS substrate. However, the E-SERS substrates require auxiliary equipment to provide the electrical potential, and most of them are non-flexible structure, which limits the application of E-SERS in the portable, in-situ and fast detection area. Here, we developed an electric field-modulated SERS substrate based on the piezoelectric effect by combining the PVDF (piezoelectric-modulated layer) and Ag nanowires (AgNWs) (SERS active layer) and investigated the SERS activity in experiment and theory. The enhanced electric field and the tunable plasmon resonance induced by the piezoelectric effect provide the additional enhancement for the SERS signal. Furthermore, we fabricated a SERS active ring with a piezoelectric field-modulated substrate and achieved the in-situ detection of glucose with a non-invasive method. This work provided innovation for the E-SERS and could greatly promote the development of the in-situ, wearable and intelligent sensors.

Hyperbolic metamaterials (HMMs), supporting surface plasmon polaritons (SPPs), and highly confined bulk plasmon polaritons (BPPs) possess promising potential for application as surface-enhanced Raman scattering (SERS) substrates. In the present study, a composite SERS substrate based on a multilayer HMM and gold-nanoparticle (Au-NP) layer was fabricated. A strong electromagnetic field was generated at the nanogaps of the Au NPs under the coupling between localized surface plasmon resonance (LSPR) and a BPP. Additionally, a simulation of the composite structure was assessed using COMSOL; the results complied with those achieved through experiments: the SERS performance was enhanced, while the enhancing rate was downregulated, with the extension of the HMM periods. Furthermore, this structure exhibited high detection performance. During the experiments, rhodamine 6G (R6G) and malachite green (MG) acted as the probe molecules, and the limits of detection of the SERS substrate reached 10⁻¹⁰ and 10⁻⁸ M for R6G and MG, respectively. Moreover, the composite structure demonstrated prominent reproducibility and stability. The mentioned promising results reveal that the composite structure could have extensive applications, such as in biosensors and food safety inspection.

We model optical bistability in all-dielectric guide-mode resonance grating (GMR) nanostructures working at quasi-bound states in the continuum (BICs). The complementary metal-oxide-semiconductor (CMOS) compatible material silicon nitride (SiN) is used for the design of nanostructures and simulations. The ultra-low threshold of input intensity in the feasible nanostructure for nanofabrication is obtained at the level of ~100 W/cm² driven by quasi-BICs. Additionally, the resonance wavelength in the GMR nanostructure can be widely tuned by incident angles with the slightly changed Q-factor that enables the optical bistable devices to work efficiently over a wide spectrum. The impact of the defects of grating that may be introduced in the fabrication process on the optical properties is discussed, and the tolerance of the defects to the optical performance of the device is confirmed. The results indicate that the GMR nanostructures of broadband and ultra-low threshold optical bistability driven by quasi-BICs are promising in the application of all-optical devices.

We theoretically demonstrate a low threshold and widely tunable spaser based on a plasmonic nanostructure consisting of two sets of disk-rings (TSDR). The TSDR nanostructure supports two dark surface plasmons (SPs), which are excited simultaneously by two bright SPs at Fano dips. The two dark SPs support lower effective mode volume, higher quality factor and higher Purcell factors. When the dark SPs serve as the pumping and lasing mode of a spaser, the spaser has a lower lasing threshold, a higher pump absorption efficiency and a lower threshold absorbed pump power than the spaser based on a bright SP. In addition, the lasing and pumping wavelengths of the spaser proposed in this article can each be tuned over a very wide wavelength range. Our results should be significant for the development of spasers.