Large Area Microfluidic Sensors Based on Flat-Optics Au Nanostripe Metasurfaces

Flat-optics microfluidic sensors based on one-dimensional Au nanostripe lattices are homogeneously fabricated over a large area (cm^2), demonstrating a cost-effective approach able to combine scalable functionalization of transparent templates, fast and compact optical detection, and competitive refractive index sensing capabilities. Laser interference lithography, combined with controlled metal evaporation, allows us to tailor the periodicity and the morphology of the plasmonic nanoantenna gratings supporting Rayleigh anomalies (RAs). By combining the nanofabrication with the degree of freedom of the tilt, we show very easy and precise tuning of RAs propagating at the air− and at the substrate−lattice interface, achieving resonant coupling with the plasmonic resonance of individual Au nanostripes. Under this condition, we show the capability to tailor narrowband Fano-like resonances by exploiting a very simple optical extinction setup, which enabled large-area microfluidic sensing. We show a large-area refractive index sensitivity as high as 275 nm/RIU evaluated over a wide RI range (∼10^−1), a competitive figure with respect to the performance of state-of-the art lithographic sensors. The efficiency of this easy and scalable method suggests these flat-optics nanosensors as good candidates for cost-effective biosensing, optical spectroscopies and diagnostics.