Recent developments of flexible and transparent SERS substrates

Surface enhanced Raman scattering (SERS) is a sensitive chemical analysis technique, and the huge Raman enhancement is mainly contributed by surface plasmon resonance of the metal nanoparticles immobilized on support substrates. Compared with the SERS-active nanostructures on rigid supports, the ones on flexible and transparent films provide a non-invasive SERS detection by being attached onto the surface of interest. Moreover, these SERS-active films could be easily reused. Owing to these advantages, these films have attracted much attention in many fields in the past few years. In this review, we have summarized and discussed the recent developments in the fabrication and application of transparent and flexible SERS-active films. First, the fabrication techniques are summarized and divided into four categories, in situ wet chemical synthesis of plasmonic structures, physical deposition of plasmonic metals, nanoparticle adsorption and nanoparticle embedding, based on how plasmonic structures are constructed on flexible substrates. After that, the applications of these SERS-active films are reviewed. They could be used for qualitative and quantitative detection of small molecules, in situ and non-invasive detection of chemical compounds on solid surfaces, spatial mapping of chemical information, as well as for fundamental study. Finally, the challenges and perspectives of this field are presented. It is believed that this review will be helpful for the design, fabrication and application of novel highly efficient SERS systems, especially for real-life applications.