Refractometric and colorimetric index sensing by a plasmon-coupled hybrid AAO nanotemplate

Abstract

Facile optical sensors capable of measuring a small change in an analyte’s refractive index have been highlighted as the demand for environmental and Internet-of-Things (IoT) applications increases. In this work, we demonstrate a large-area refractive index sensor capable of refractometric and colorimetric sensing with a plasmon-coupled hybrid nanotemplate of anodic aluminum oxide (AAO). The nanotemplate enhances the figure-of-merit and sensitivity due to the coupled mode of the Fabry–Perot microcavity and metallic nanosurfaces. The increased mode confinement and interaction between AAO pores and analytes show highly modulated reflection spectra, which enable a refractive index sensitivity up to 348 nm per RIU and a figure-of-merit value up to 27.7. Also, the vivid color change induced from infiltrated analytes allows a colorimetric sensing performance up to RIU/ΔE ∼ 0.006 according to CIELab 1931 analysis. The key features of our device are simultaneous applications to superb dual (refractometric and colorimetric) sensing schemes by the plasmon-coupled hybrid AAO nanotemplate.