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 MoS edge-active sites induced from annealing the Ag film on the surface of the MoS. Furthermore, the composite structure of Au-Ag bi-metal nanoparticles (NPs)/MoS 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 × 10) 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 and 10 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 M using the proposed SERS substrate that has the potential to be a food security sensor.

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provide more hot spots, which are introduced by the electromagnetic mechanism (EM). By the virtue of their larger specific surface area and periodic structure, 3D SERS substrates can effectively amplify the optical field around metal nanoparticles (NPs), thereby enhancing the Raman signal. Moreover, the 3D structure of these substrates is beneficial for the enrichment of probe molecules around metal nanoparticles; as a result, one can still obtain a high Raman signal, even under an ultralow concentration. Consequently, an increasing number of researchers are now focusing on the design and fabrication of 3D SERS substrates.To make full use of the merits of the 3D structure, SERS substrates based on 2D materials and metal nanoparticles have been combined and proposed. [23,24] In these 3D SERS substrates, the 3D structure can fully utilize the 3D focal volume of the incident beam and increase the density of the metal nanoparticles. Furthermore, introduction of the 2D material can act as an atomically thick SERS substrate, [25] perfect absorbent layer of molecules, [26] excellent sub-nanometer spacer, [27] and passivation layer for metal, [28,29] and introduce enhancements via a chemical mechanism (CM). Previously, a 3D SERS substrate based on graphene covering a pyramid-shaped Au structure was reported to achieve high enhancement. [30] While the integration of graphene and pyramid-shaped Au was successfully implemented, this 3D SERS substrate was not flexible and did not meet with the requirements when detecting probe molecules on an arbitrary curvilinear surface.Therefore, transformation of these stiff 3D substrates into flexible structures via using various methods has been investigated extensively. Leem et al. reported 3D crumpled graphene-AuNPs hybrid structures for SERS applications using a mechanical self-assembly strategy on a thermally activated polymer. [31] Similarly, Lee et al. fabricated a rippled graphene structure on a polystyrene substrate using a thermal rippling process and demonstrated the increased plasmonic coupling and higher density of the hot spots on the rippled nanostructure. [32] Kumar et al. presented a flexible SERS sensor by depositing Ag on structured polydimethylsiloxane using a Taro leaf as the template and achieved highly sensitive detection for malachite green. [33] Moreover, to fabricate a flexible 3D SERS substrate, the transfer printing technique, [34] shadow Substrate design has attracted much interest in development of an effective surface enhanced Raman scattering (SERS) sensor. A flexible SERS substrate with excellent performance needs to be sensitive to details of the preparation process; this sensitivity represents a significant challenge for practical applications as opposed to laboratory research applications. Here, a 3D flexible plasmonic structure, AgNPs@MoS 2 /pyramidal polymer (polymethyl methacrylate), is fabricated using a simple and lowcost method. Using experiments and theoretical simulations, the SERS performance of the proposed substrate is assessed in terms of ...

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 × 10, 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.