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Wettability modification is an effective way in tailoring hotspots in surface Raman scattering (SERS) nowadays. However, due to the theoretical contradiction between hydrophobic and hydrophilic strategies, opposite views are usually put forward in building SERS structures. To realize the integration of hydrophobicity and hydrophilia in the same substrate, a wettability-switchable SERS architecture composed of heterostructured CuO@ZnO@Ag biomimetic nano Setaria (NS) has been designed and prepared in this paper. Experimentally, the structure shows impressive SERS performance under both hydrophobic and hydrophilic states. The limit of detection approaches even to single-molecule level and the lowest relative standard deviation is only ca 9.8%. Finite-different time-domain simulations and experimental analyses were systemically made to unearth the mechanism deep behind. Besides, owing to fine quantifiability, the CuO@ZnO@Ag NS shows promising potential in the detection of trace pesticide and deoxyribonucleic acid. This work provides a new idea for integrating the strategies of 'concentration' and 'decentralization', endowing SERS structure with wider application, and is also meaningful for other surface sciences. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

An efficient electrospun aligned surface enhanced Raman scattering (SERS) and maize-like substrate of polyvinyl alcohol (PVA) composite and Ag colloid nanofibers decorated with thermal evaporated Ag nanoparticles (AgNPs) has been developed by taking advantage of electrostatic interactions. The synergistic effects of the evaporated AgNPs (niblets) and the Ag colloid in PVA (corncob) could arouse strong electromagnetic field between the lateral and vertical nanogaps which has been demonstrated by experiment and finite-different time-domain (FDTD) simulation. In this experiment, the aligned nanofibers possesses an excellent sensitivity by detection of crystal violet (CV) and malachite green (MG) molecule at low concentration. Moreover, the proposed flexible SERS sensor was measured with outstanding uniformity and reproducibility. We also carried out in-situ electrospinning on a curved surface to detect the mixture of Sudan I, CV and MG molecule, which demonstrates that flexible SERS sensor, has enormous potential in accurate and in-situ detection on the complex geometric structure. [ABSTRACT FROM AUTHOR]

Highlights • 3D hybrid MoS2/AgNPs/inverted pyramid PMMA resonant cavity system was proposed for flexible SERS sensor. • The SERS enhanced principle of the above system was investigated in experiment and theory. • The flexible SERS substrate housed at the optical fiber was used to remotely detect the toxic malachite green solution. Abstract It is widely accepted that resonant cavity system represents the effective laser utilization due to the back and forth reflection and the electric field energy storage. Here, a three-dimensional (3D) hybrid MoS 2 /AgNPs/inverted pyramid polymethyl methacrylate (iPPMMA) resonant cavity system as a flexible surface enhanced Raman scattering (SERS) sensor was investigated in experiment and theory. The obtained resonant cavity between MoS 2 , iPPMMA and the plasmonic silver nanoparticles offers the tremendous local near-field enhancements, which is manifested using the finite-difference time-domain (FDTD) theoretical simulation. Additionally, by virtue of the lower light absorption, the iPPMMA gains the advantage over pyramid Si (PSi) in term of enhancing local electric field. The synergistic effects of MoS 2 , iPPMMA and AgNPs can generate the 3D dense hot spots and extremely contribute to the excellent ultrasensitivity, stablity, reproducibility and recyclability of the proposed flexible SERS sensor. Moreover, the fabricated MoS 2 /AgNPs/iPPMMA hybrid structure was housed at the end of the optical fiber to remotely detect the toxic mixtures solution, which demonstrates our flexible SERS sensor has enormous potential to be applied in food safety field. [ABSTRACT FROM AUTHOR]

We report a simple method to fabricate Ag 2 O@Ag core-shell nanostructure employed as SERS (surface enhanced Raman scattering) active substrate. The Ag 2 O shell was fabricated via the oxidation of AgNPs with the assist of laser irradiation in atmosphere. In this way, the prepared Ag 2 O@Ag hybrid system possesses ultrasensitivity, homogeneity, reproducibility and chemical stability by virtue of ultra-thin inner shell. The minimum detectable concentration of R6G was presented as low as 10 −11 M. The enhancement factor of Ag 2 O@Ag core-shell nanostructure using R6G as probe molecules was found to be as high as 6 × 10 7 . Furthermore, the flexible Ag 2 O@Ag/PMMA SERS substrate were first presented and the SERRS (surface enhanced resonance Raman scattering) spectra of the R6G on this substrate were investigated. The characteristic peaks of R6G with concentration from 10 −5 –10 −11 M can be also easily observed by detecting from both sides of the flexible substrate. A good linear response between SERRS intensity and R6G concentration from 10 −5 to 10 −11 M was obtained. For practical application, the Ag 2 O@Ag/PMMA hybrids flexible SERS substrate was used for real-time and in-situ detection of chlorpyrifos with 10 −7 M on cucumber and apple peels. These results are exactly consistent with the DFT simulation on chlorpyrifos pesticide and confirm that the Ag 2 O@Ag/PMMA hybrids flexible SERS substrate is highly promising for food safety field in the future. [ABSTRACT FROM AUTHOR]

Graphene–metal substrates have received widespread attention due to their superior surface-enhanced Raman scattering (SERS) performance. The strong coupling between graphene and metal particles can greatly improve the SERS performance and thus broaden the application fields. The way in which to make full use of the synergistic effect of the hybrid is still a key issue to improve SERS activity and stability. Here, we used graphene as a chemical mechanism (CM) layer and Ag nanoparticles (AgNPs) as an electromagnetic mechanism (EM) layer, forming a CM–EM unit and constructing a multi-layer hybrid structure as a SERS substrate. The improved SERS performance of the multilayer nanostructure was investigated experimentally and in theory. We demonstrated that the Raman enhancement effect increased as the number of CM–EM units increased, remaining nearly unchanged when the CM–EM unit was more than four. The limit of detection was down to 10−14 M for rhodamine 6G (R6G) and 10−12 M for crystal violet (CV), which confirmed the ultrahigh sensitivity of the multilayer SERS substrate. Furthermore, we investigated the reproducibility and thermal stability of the proposed multilayer SERS substrate. On the basis of these promising results, the development of new materials and novel methods for high performance sensing and biosensing applications will be promoted. [ABSTRACT FROM AUTHOR]

This paper introduces a three-dimensional (3D) pyramid to the polymers-plasmonic hybrid structure of polymethyl methacrylate (PMMA) composite silver nanoparticle (AgNPs) as a higher quality flexible surface-enhanced Raman scattering (SERS) substrate. Benefiting from the effective oscillation of light inside the pyramid valley could provide wide distributions of 3D "hot spots" in a large space. The inclined surface design of the pyramid structure could facilitate the aggregation of probe molecules, which achieves highly sensitive detection of rhodamine 6G (R6G) and crystal violet (CV). In addition, the AgNPs and PMMA composite structures provide uniform space distribution for analyte detection in a designated hot spot zone. The incident light can penetrate the external PMMA film to trigger the localized plasmon resonance of the encapsulated AgNPs, achieving enormous enhancement factor (~ 6.24 × 10 8 ). After undergoes mechanical deformation, the flexible SERS substrate still maintains high mechanical stability, which was proved by experiment and theory. For practical applications, the prepared flexible SERS substrate is adapted to the in-situ Raman detection of adenosine aqueous solution and the methylene-blue (MB) molecule detection of the skin of a fish, providing a direct and nondestructive active-platform for the detecting on the surfaces with any arbitrary morphology and aqueous solution. [ABSTRACT FROM AUTHOR]

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@MoS2/pyramidal polymer (polymethyl methacrylate), is fabricated using a simple and low‐cost method. Using experiments and theoretical simulations, the SERS performance of the proposed substrate is assessed in terms of its high enhancement factor, ultrasensitivity, quantifiability, reproducibility, stability, and reusability. Finally, the ultralow in situ detection limits of the standard melamine solution and melamine in milk are found to be 10−10 and 10−6m, respectively, which meet the demand for real applications in the food security field. 3D flexible plasmonic structure, AgNPs@MoS2/pyramidal polymer fabricated using a simple and low‐cost method, was demonstrated with high effective surface enhanced Raman scattering (SERS) performance from experiment and theory. The in‐situ detection limits of the standard melamine solution and melamine in milk are 10−10 and 10−6m, respectively, which meet the demand for real food security field applications. [ABSTRACT FROM AUTHOR]

Here we designed a new kind of SERS substrate referred to as a MoS 2 -coated Cu nanopaticles (MoS 2 @CuNPs) substrate for R6G detection. The Cu nanoparticles wrapped by a thin MoS 2 film were directly synthesized on flat quartz by two annealing process in a mixture of argon and hydrogen. Signals from a MoS 2 @CuNPs SERS substrate were also demonstrated to have interesting advantages over pure CuNPs SERS, in terms of the excellent linear relationship between Raman intensity and analyte concentration, strongly background fluorescence quenching and being more stable against photo-induced damage and oxidation. The minimum detectable concentrations of R6G on MoS 2 @CuNPs hybrids can be as low as 10 −9 M which is one order lower than that on the pure CuNPs substrates. This synthetic approach is facile, scalable and applicable to the MoS 2 film compound with other metals such as Ag, Au etc. [ABSTRACT FROM AUTHOR]