Flexible surface-enhanced Raman scattering substrates: A review on design strategies, fabrication technologies, and applications

Surface-enhanced Raman scattering (SERS) has drawn great attention due to its sensitive detection and fingerprint identification. Plasmonic structures built on supporting substrate to integrate SERS devices have broadened its practical applications. Compared with rigid materials for supporting substrate, flexible materials have received great interest, in terms low-cost, non-invasive, and easy-operation, especially for curved surface samples. Herein, an in-depth exploration of the latest progress in flexible SERS substrates was presented, which focused on both design strategies for optimizing SERS signal enhancement and the fabrication techniques that enable large-scale production. We introduced two novel approaches for manipulating the hotspot distribution in flexible SERS substrates, a critical factor for improving signal sensitivity and reproducibility, which was underexplored in previous reviews. Furthermore, we provided a comprehensive overview of various flexible materials-based SERS substrates, including polymers, cellulose, and other biomaterials, along with their typical fabrication methods. This review also highlights cutting-edge applications of FSS in biosensors, in-situ detection of food pesticides, environmental pollutants monitoring and microfluidic technology with an emphasis on practical application challenges, such as substrate uniformity, stability, and scalability. It is believed that this review would help the researchers in diverse fields related to materials, nanophotonics, and SERS to design and develop novel FSS with highly sensitive and simply reproducible toward real-world applications in chemical and biological sensing.