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Putrescine and cadaverine are significant volatile indicators used to assess the degree of food spoilage. Herein, we propose a micro-nano multi cavity structure for surface-enhanced Raman spectroscopy (SERS) to analyze the volatile gas putrescine and cadaverine in decomposing food. The MoS 2 nano-flowers are inserted into a PVDF micro-cavity through in-situ growth, followed by vacuum evaporation technology of Ag nanoparticles to form an Ag/MoS 2 nano-flower cavity/PVDF micron-bowl cavity (FIB) substrate. The micro-nano multi cavity structure can improve the capture capacity of both light and gas, thereby exhibiting high sensitivity (EF = 7.71 × 10 7 ) and excellent capability for gas detection of 2-naphthalenethiol. The SERS detections of the putrescine and cadaverine are achieved in the spoiled pork samples with the FIB substrate. Therefore, this substrate can provide an efficient, accurate, and feasible method for the specific and quantitative detection in the food safety field.

In this study, the output energy in topological insulators (TIs)-based Erbium-doped fiber laser (EDFL) was improved using two strategies: bidirectional pumped laser cavity and saturable absorber (SA) with high damage threshold and large modulation depth. Using the chemical vapor deposition (CVD) method, Bismuth Selenide (Bi 2 Se 3 ) film was synthesized and improved to a SA. Employing this CVD-Bi 2 Se 3 SA in an EDFL, bright and bright-dark soliton operations were achieved. The average output power/pulse energy was 82.6 mW/48.3 nJ and 81.2 mW/47.5 nJ, respectively. The results demonstrate that CVD-Bi 2 Se 3 can act as an excellent performance material to improve output power performance in TISA-based EDFL.

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 2 edge-active sites induced from annealing the Ag film on the surface of the MoS 2 . Furthermore, the composite structure of Au-Ag bi-metal nanoparticles (NPs)/MoS 2 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 9 ) 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.

The highly enhanced local electromagnetic field occurring through nanometer gap between the plamonic nanostructures provides the dominant contribution in surface enhancement Raman scattering (SERS) enhancement. Thence, we designed the remarkable SERS platform (AuNPs/WS 2 @AuNPs hybrids) by introducing bilayer WS 2 film as the precise nanospacer. Bilayer WS 2 film can realize the facile and tight combination with AuNPs via the thermal decomposition approach. Dense three-dimension (3D) hot spots provided by this hybrid plasmonic nanostructures are responsible for the extremely satisfying SERS performances. Using rhodamine 6G (R6G) as the probe molecules, the AuNPs/WS 2 @AuNPs hybrids perform the excellent sensitivity with the minimum detectable concentration as low as 10 -11 M. Uniform and reproducible SERS signals illustrate that the synthesized SERS hybrids perform the splendid spot-to-spot reproducibility (RSD~5.4%) and substrate-to-substrate reproducibility (RSD~5.7%). The stability of AuNPs and the protection of WS 2 film endow this hybrid plasmonic nanostructures with the brilliant anti-oxidation stability. Moreover, the enhanced electric field distribution simulated with the COMSOL software proves the remarkable SERS performance in theory. Therefore, AuNPs/WS 2 @AuNPs substrate not only widens the SERS research filed of WS 2 , but also shows vast potential as excellent SERS sensor for practical applicability.