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Surface-enhanced Raman scattering (SERS) is a powerful tool for trace substance detection and analysis. However, traditional SERS detection based on substrates usually separates sampling and detection, which are time consuming and lack portability for practical applications. In this study, we developed a SERS fiber optic probe using a simple and efficient laser-induced evaporation assembly method. By direct immersion of the fiber in a microliter colloidal solution of silver nanocubes (Ag NCs) under laser induction, a monolayer of uniform and dense Ag NCs was modified on the end face of the optical fiber. The fabricated SERS fiber optic probe demonstrated excellent reproducibility and stability with a detection limit of less than 10–8 M for the 4-mercaptobenzoic acid (4-MBA), with the intensity of its two characteristic Raman peaks showing a high linear correlation with the logarithm of the concentration. Furthermore, by combining Ag NCs with bromide ions, the Ag-Br NCs fiber optic probe we fabricated and exhibited outstanding performance in detecting organic pollutants polycyclic aromatic hydrocarbons (PAHs). This work may have potential significance in broadening the application field of SERS fiber-optic probes.

Hydrogen detection is crucial for the forthcoming hydrogen economy. Here, we present a visual, ultrasensitive, optical hydrogen sensor based on a tunable Fabry–Pérot (FP) resonator, which can fully release the volume expansion of palladium during hydrogenation and transfer this volume expansion into an optical signal. The FP resonator consists of a suspended polymethylmethacrylate/palladium (PMMA/Pd) bilayer on a gold (Au) square-hole array. The bottom of the gold square hole and hydrogen-sensitive PMMA/Pd bilayer form a dynamically tunable FP resonator. When hydrogen gas (H2) is loaded, the hydrogen-induced lateral expanding stress concavely deforms the suspended bilayer downward to the substrate, narrowing the metal–air–metal gap at the center of the hole, and finally leading to a spectral blue shift. Our experimental results show a giant spectral shift of 279 nm with a reflectance variation of 57% on exposure to 0.6% H2mixed with air. Such an ultrahigh optical response results in a significant color change, enabling visual hydrogen detection. In addition, the sensor has a H2detection limit down to 0.1% and good recyclability. These advantages indicate that the sensor has excellent potential for hydrogen sensing applications.

Compared with conventional rigid devices, the elastic substrates integrated with functional components offer various advantages, such as flexibility, dynamic tunability, and biocompatibility. However, the reliable formations of 2D nanoparticles, nanogaps, and 3D nanostructures on elastic substrates are still challenging. The conventional transfer method plays an important role in the fabrication of microstructures on elastic substrates; however, it could not fabricate structures with feature size less than a few micrometers. In this article, we have developed a flexible technique based on the “metal-assisted transfer” strategy. The key concept is to introduce a metal film as an assistant layer between nanostructures and silicon substrates to help the fabrication of nanostructures which cannot be successfully transferred in the conventional transfer method. Various 2D nanostructures, which are difficult to achieve on elastic substrates, could be reliably defined using this approach. The desired gap distances and even sub-10 nm metal gaps between adjacent nanoparticles can be controllably achieved. Moreover, 3D nanostructures can be directly assembled from the prestrained 2D precursors based on the developed technique. Comparing with the previous reports, our fabrication method contains only a one-step transfer process without selective bonding or a second transfer process. Significantly, the 3D nanostructures presented here are 2 orders of magnitude smaller than the state-of-the-art mechanically assembled 3D structures in unit cell size. The proposed method may become a mainstream technology for the nano-optics and ultracompact optoelectronic devices due to its multifunctionalities and superior advantages in achieving tunable nanoparticles as well as 3D nanostructures.