Au/SiO₂-Nanolaminated Plasmonic Nanoantennas as Refractive-Index-Insensitive and Transparent Surface-Enhanced Raman Spectroscopy Substrates

Surface-enhanced Raman spectroscopy (SERS) has become a powerful technique for ultrasensitive biochemical detection providing molecular fingerprint information. Due to the strong dependence of surface plasmon resonance wavelength on plasmonic nanostructures’ surrounding refractive index (RI), SERS enhancement factors (EFs) at hotspots are sensitive to changes in background RI, which is detrimental to quantitative SERS biochemical analysis in real-world applications with spatially and temporally varying RI matrices. This work reports on a tapered-shape nanolaminate plasmonic nanoantenna (TNLNA) platform that supports multiple, spatially overlapped, hybridized magnetoelectric localized surface plasmon modes revealing high SERS EFs (>107) and an insensitivity to background RI variations (between 1.30 and 1.60). Furthermore, we demonstrate that the uniform arrays of TNLNAs can be manufactured on flexible transparent polymer films to achieve backside-excitable and reversible SERS measurements for in situ label-free glucose monitoring on a skin phantom.