Flexible Multilayer Plasmonic Films for Biosensing and Photoemitting Applications.

Flexible plasmon metasensor devices describe the use of multiple Ag/Al₂O₃/mica layers for tunable plasmonic resonances and are a promising research direction. Here, we report on a flexible Ag/Al₂O₃/mica multilayer platform and its excellent performance on flexible biosensors and photon-emitting devices. In our approach, muscovite (mica) was adopted as a single-crystal substrate due to its optical transparency and mechanical flexibility. The Ag/Al₂O₃/mica multilayer film is characterized by X-ray diffraction and transmission electron microscopy. Optical, plasmonic, and biosensing studies of Ag/Al₂O₃/mica multilayers are performed for detailed understanding. A combination of optical absorption, numerical simulations, and optical reflectance measurements has confirmed the biosensor performance. Two kinds of flexible plasmonic device applications are reported here, including (1) plasmonic biosensors with high refractive index sensitivities and (2) significantly enhanced spontaneous photoluminescence (PL) of monolayer tungsten disulfide (WS₂) spectra. We found that the PL emission under 0.4 mm^-1 curvature bending state increased to 16% compared to the unbent state and redshift of 60 meV/% strain in the emission of WS₂ monolayer. Furthermore, the Ag/Al₂O₃/mica multilayer film displays robust stability and strong endurance up to a bending curvature of 0.4 mm^-1. This study shows great potential to be used for biosensors and flexible optoelectronics.