To improve the drawback of surface-enhanced Raman scattering (SERS) sensors that are sensitive to excitation angles and realize the monitoring of contaminants in complex environments, we have proposed and prepared a cascaded wire-in-cavity-in-bowl (WICIB) structure on flexible polydimethysiloxane, with feasibility for plasmonic coupling. We demonstrated that the WICIB structure can serve as a highly sensitive, homogeneous, and stable SERS substrate for conventional detection. The plasmonic coupling and distribution of the enhanced electromagnetic field were evidently proven by finite element simulations, and the strong electromagnetic field was regulated around the wire and inside the cavity, which is very beneficial for the polydirectional and in situ detection. By virtue of the triple synergistic enhancement effect and unique optical properties, we successfully achieved the in situ detection of the residual pollutant molecules, ziram and 2-naphthalenethiol, in microdroplets of apple juice and lake water. Accordingly, such a flexible SERS sensor exhibits great potential in on-site environmental monitoring.

The combination of metallic nanoparticles (NPs) with semiconductors used as surface-enhanced Raman scattering (SERS) substrates have been widely reported. However, the additional enhancements provided by the semiconductors are impressively small and have little effect on the SERS signal compared with that from the metallic NPs alone. Herein, thermoelectric semiconductor material gallium nitride (GaN) and silver nanoparticles (Ag NPs) are combined to create an electric-field-induced SERS (E-SERS) substrate, which further improves the SERS signal intensity by an order of magnitude compared to that without electric field induction. Based on the chemical enhancement induced by the thermoelectric potential, the presented E-SERS substrate realizes the detection over a broad kind of molecules, even with small Raman scattering cross sections.We show that the thermoelectric potential could regulate the charge exchange between GaN and Ag NPs and then shift the Fermi level of the Ag NPs over a wide-ranging distribution, which could increase the resonant electron transition probabilities with the detected molecules. Furthermore, the E-SERS substrate is also realized to monitor and manipulate the plasmon-activated redox reactions. Based on the finite element calculations, a detailed and comprehensive theoretical analysis is conducted to deepen the understanding of the chemical SERS and plasmon-activated photocatalyst mechanism.

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