Flexible surface-enhanced Raman scattering substrates toward sampling approaches for on-site sensing and diagnosis applications

Over the past 45 years, the discovery of surface-enhanced Raman scattering (SERS), which enhances the Raman scattering of molecules absorbed on or near nanostructured metal surfaces, has brought significant potential as a powerful spectroscopic and analytical technique for various fields of ultrasensitive sensing applications. In preference to rigid substrates, recent advances in the development of flexible SERS sensors have enabled the fulfillment of practical on-site sensing and diagnostic applications with rapid and efficient sampling approaches. In this review, we summarize and discuss the most recent developments in flexible SERS substrates for on-site sensing and diagnosis over the past 4 years. We highlight the three main categories of flexible SERS sensors based on their sampling methods, including drop-and-dry, collection/swabbing, and wearable/attachable approaches. The use of substrate materials and the design of sensing platforms for sampling regarding various targets are reviewed. Finally, we discuss the challenges and perspectives of flexible SERS sensors for future developments.