Development of a polymer/TiO2 hybrid two-dimensional photonic crystal for highly sensitive fluorescence-based ion sensing applications

Abstract

In this study, we developed a polymer/TiO2 hybrid two-dimensional photonic crystal (2D-PhC) optical ion sensor that shows fluorescence enhancement based on the matching of the fluorescence wavelength and the confinable wavelength of a 2D-PhC. The polymer/TiO2 hybrid PhC was fabricated from a TiO2 pillar array, where the interspace was filled with a polymer containing a fluorescent dye. We developed a method of fabricating the TiO2 pillar array based on nanoimprint lithography using liquid phase deposition. The polymer/TiO2 hybrid PhC was fabricated on a poly(ethylene terephthalate) (PET) film. Thus, it can be easily cut because of its high flexibility and used for ion sensing applications.By using a fluorescent dye-containing polymer (poly(methyl methacrylate), PMMA) for the fabrication of the polymer/TiO2 hybrid PhC, the fluorescence intensity was drastically (25 times) increased. Subsequently, we used an ion-sensing polymer composed of plasticized poly(vinyl chloride) (PVC), a fluorescent dye, and ion recognition elements in the polymer/TiO2 hybrid PhC to enable its use as a highly sensitive ion sensor. As a result, the ion sensor based on the plasticized-PVC/TiO2 hybrid PhC exhibited four times greater fluorescence intensity compared with that based on the plasticized PVC without the PhC structure.