It is very vital to construct the dense hot spots for the strong surface-enhanced Raman scattering (SERS) signals. We take full advantage of the MoS₂ edge-active sites induced from annealing the Ag film on the surface of the MoS₂. Furthermore, the composite structure of Au-Ag bi-metal nanoparticles (NPs)/MoS₂ hybrid with pyramid structure is obtained by the in situ grown AuNPs around AgNPs, which serves the optimal SERS performance (enhancement factor is ~9.67 × 10⁹) in experiment. Due to the introduction of AuNPs with the simple method, the denser hot spots contribute greatly to the stronger local electric field, which is also confirmed by the finite-different time-domain (FDTD) simulation. Therefore, the ultralow limit of detection (the LOD of 10⁻¹³ and 10⁻¹² M respectively for the resonant R6G and non-resonant CV), quantitative detection and excellent reproducibility are achieved by the proposed SERS substrate. For practical application, the melamine molecule is detected with the LOD of 10⁻¹⁰ M using the proposed SERS substrate that has the potential to be a food security sensor.

Various flexible SERS sensors have attracted widespread concern in performing the direct identification of the analytes adsorbed on arbitrary surfaces. Here, a sample method was proposed to integrate plasmonic nanoparticles into polydimethylsiloxane (PDMS) to fabricate flexible substrate for the decoration of silver nanoparticles (AgNPs). The flexible SERS sensor based on AgNPs/AgNPs-PDMS offers highly sensitive Raman detection with enhancement factor up to 8.3 × 10⁹, which can be attributed to the integrative effects from both the increase of the light absorption of the embedded AgNPs in PDMS substrate and the EM enhancement from the adjacent top-top, bottom-bottom and top-bottom AgNPs. After undergoing the cyclic mechanical deformation, the SERS substrate still maintains high mechanical stability and stable SERS signals. However, upon stretching the flexible substrate, there was an amusing phenomenon that SERS signals can be highly increased, which results from that the reduction of lateral nanogaps between top and bottom of the PDMS boundary strengthens the trigger of the plasmon coupling as demonstrated by the simulated result. This result reveals that the tuning and the coupling of the electromagnetic fields can be effectively controlled by the macroscopic mechanical solicitation. That will have an important significance for practical applications in strain-dependent sensors and detectors.

MoS₂-based heterostructures have received increasing attention for not only surface-enhanced Raman scattering (SERS) but also for enhanced photoelectrocatalytic (PEC) performance. This study presents a hydrothermal method for preparing vertical MoS₂ nanosheets composed of in situ grown AuNPs with small size and chemically reduced AgNPs with large size to achieve the synergistic enhancement of SERS and PEC properties owing to the size effect of the plasmonic structure. Compared with pristine MoS₂ nanosheets and unitary AuNPs or AgNPs composited with MoS₂ nanosheets, the ternary heterostructure exhibited the strongest electromagnetic field and surface plasmon coupling, which was confirmed by finite-difference time-domain (FDTD) simulation and absorption spectra. In addition, the experimental results confirmed the outstanding SERS enhancement with an EF of 1.1×10⁹, and the most efficient hydrogen evolution reaction (HER) activity with a sensitive photocurrent response, attributing to the multiple surface plasmonic coupling effects of the Au-Ag bimetal and efficient charge-transfer process between MoS₂ and the bimetal. That is, it provides a robust method for developing multi-size bimetal-semiconductor complex nanocomposites for high-performance SERS sensors and PEC applications.

A D-shape plastic optical fiber (D-POF) surface plasmon resonance (SPR) biosensor based on the graphene/Au film (G/Au) was proposed and experimentally demonstrated for detection of DNA hybridization process. To improve the detection performance of SPR sensors, the Physical Vapor Deposition (PVD) method was used to evaporate the Au film directly onto the graphene grown on copper foil, and the Au film acted as a role of traditional Polymethyl Methacrylate (PMMA). The process made graphene and Au film form seamless contact. Next, the G/Au was transferred onto the D-shape fiber together. We explored the G/Au SPR sensor by using the finite element method (FEM) and obtained the optimum materials thickness to form configuration. Compared to other plastic optical fiber experiments, the proposed sensor’s sensitivity was improved effectively and calculated as 1227 nm/RIU in a range of glucose solution. Meanwhile, our proposed sensor successfully distinguishes hybridization and single nucleotide polymorphisms (SNP) by observing the resonance wavelength change. It also exhibits a satisfactory linear response (R² = 0.996) to the target DNA liquids with respective concentrations of 0.1nM to1µM, which shows this method’s wide potential in medical diagnostics.

An Au film/graphene D-shaped plastic optical fiber (D-POF) functionalized with dopamine-binding aptamer (DBA) was proposed to achieve a sensitive and specific detection of the small molecule dopamine. The surface plasmon resonance sensor combines the virtues of a D-shaped fiber, the transfer of graphene via gold film, and the amplification of the refractive index with the conformational transformation of DBA. The sensitivity of the Au film/graphene D-POF sensor (1539 nm/RIU) is higher than that without graphene in ethanol solution. The dopamine concentrations of 10 ⁻¹⁰ M to 10 ⁻⁶ M were measured. And the decoration of DBA onto graphene for dopamine detection with a good linearity was verified in experiments. The proposed sensor possesses high sensitivity and specificity, which will provide good application prospects for the development of biosensing in disease treatment.