Flexible, Transparent, and Microfluidic-Compatible Wafer-Scale Metamaterial Sheets for Dual SEF and SERS Sensing

Integrating surface-enhanced fluorescence (SEF) and surface-enhanced Raman spectroscopy (SERS) into a single probe is a natural step forward for plasmon-enhanced spectroscopy (PES), as SEF enables enhanced fluorescent imaging for fast screening of targets, while SERS allows ultrasensitive trace molecular characterization with specificity. However, many challenges remain, e.g., the dilemma between high SEF and SERS enhancements due to the use of dielectric spacers, localized surface plasmon resonances (LSPRs) with limited band coverage that restrict the selection of fluorophores, and lack of scalability, including flexibility, transparency, and microfluidic compatibility. In this work, SEF and SERS are integrated onto a flexible, transparent, and mass-producible 6-in. wafer-scale plasmonic metamaterial sheet (PLAMS), exhibiting high SEF and SERS enhancement factors, high signal uniformity, and native microfluidic compatibility. Particularly, broadband LSPRs from ∼400 to 1000 nm are realized for extended SEF usability to a wider range of fluorophores. Maximized surface-averaged SEF and SERS enhancements (∼209 and 1.17 × 10⁶, respectively) are simultaneously achieved without the use of dielectric spacers. Signals experience only about 20% loss when probed from the backside. Using simple capillarity-driven bonding, native microfluidic integration is achieved with scalability, making it ideal for rapid prototyping toward specific applications. Dual SEF and SERS sensing of polystyrene microplastics demonstrates that the probe is capable of rapid target screening via SEF followed by in situ ultrasensitive trace molecular characterization with specificity via SERS. Single-particle SERS detection of polystyrene is successfully achieved. The presented all-in-one dual SEF and SERS sensing platform facilitates PES technology and holds promise for future large-scale, pragmatic applications.