Quantitative analysis of formaldehyde (HCHO, FA), especially at low levels, in various environmental media is of great importance for assessing related environmental and human health risks. A highly efficient and convenient FA detection method based on surface-enhanced Raman spectroscopy (SERS) technology has been developed. This SERS-based method employs a reusable and soft silver-coated TiO2 nanotube array (TNA) material, such as an SERS substrate, which can be used as both a sensing platform and a degradation platform. The Ag-coated TNA exhibits superior detection sensitivity with high reproducibility and stability compared with other SERS substrates. The detection of FA is achieved using the well-known redox reaction of FA with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT) at room temperature. The limit of detection (LOD) for FA is 1.21 × 10−7 M. In addition, the stable catalytic performance of the array allows the degradation and cleaning of the AHMT-FA products adsorbed on the array surface under ultraviolet irradiation, making this material recyclable. This SERS platform displays a real-time monitoring platform that combines the detection and degradation of FA.

A sandwich-structured noble metal-probe molecule-organic semiconductor consisting of Ag nanoparticles (NPs), 4-mercaptobenzoic acid (4-MBA) and different concentrations of poly(styrenesulfonate:poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) was prepared by layer-by-layer assembly. Intermolecular hydrogen bonding was observed to have a significant effect on the surface-enhanced Raman scattering (SERS) of Ag/4-MBA/PEDOT:PSS. Upon increasing the PEDOT:PSS concentration, the characteristic Raman band intensity of 4-MBA was enhanced. In addition, the selected b2 vibration mode was significantly enhanced due to the influence of the charge transfer (CT) mechanism. The CT degree (ρCT) of the composite system was calculated before and after doping with PEDOT:PSS; when the concentration of PEDOT:PSS was 0.8%, the SERS intensity tended to be stable, and ρCT reached a maximum. Compared with that of the undoped PEDOT:PSS system, ρCT was significantly enhanced after doping, which can be explained by the CT effect induced by hydrogen bonds. These results indicate that hydrogen bonding transfers a charge from the Fermi energy level of Ag to the lowest unoccupied molecular orbital (LUMO) of 4-MBA, and due to the resulting potential difference, the charge will continue to transfer to the LUMO of PEDOT:PSS. Therefore, the introduction of organic semiconductors into the field of SERS not only expands the SERS substrate scope, but also provides a new idea for exploring the SERS mechanism. In addition, the introduction of hydrogen bonds has become an important guide for the study of CT and the structure of composite systems.

Understanding and controlling the disorder in materials, especially the disorder caused by structural composition and doping effects, are important keys to studying the optical characteristics of materials. In this study, a SiO2–Ag–reduced graphene oxide (rGO) composite structure was prepared by a simple wet chemical method, in which Ag nanoparticles (NPs) and SiO2 were decorated onto the surface of rGO. The introduction of Si atoms can control not only the plasmon effect of Ag NPs but also, more importantly, the defect concentration of rGO. The formation of defects causes the rGO structure to enter a metastable state, which facilitates charge separation and transfer in the system. It is worth noting that changes in defect concentration can affect the energy band position of rGO; therefore, controlling the defect concentration can be used to achieve charge transfer resonance coupling. This study not only revealed the ultrahigh surface-enhanced Raman scattering activity of the substrate structure but also elucidated in detail the effect of the crystallinity of this rGO-based composite system on its optical properties.

With the development of the surface‐enhanced Raman scattering (SERS) technique, new multipurpose and multiperformance SERS‐active substrates have been developed. Semiconductor and semiconductor/metal composites show versatility and SERS activity for theoretical and practical applications. Semiconductor‐based SERS substrates with different microstructures, materials and compositions have been prepared to explore the enhancement effect on Raman signals. The discovery of the SERS enhancement effect of semiconductors makes up for the gap that SERS development is limited to metal‐based materials. Semiconductor/metal composite substrates have established preparation technology that is compatible with the characteristics of different materials to form a stable and solid substrate that can regulate the SERS enhancement mechanism. These composites establish a good model for the theoretical research of SERS, which is of great significance to explore its enhancement mechanism. In this review, various semiconductor materials are introduced as SERS‐active substrates. Versatile applications of semiconductor‐based SERS and its enhancement mechanism are also presented.

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