Plasticized Poly(vinyl chloride)-Based Photonic Crystal for Ion Sensing

In this study, we, for the first time, developed a plasticized poly(vinyl chloride) (PVC)-based two-dimensional photonic crystal (2D-PhC) optical sensor using nanoimprint lithography (NIL), which can perform highly sensitive, fast, and selective ion sensing based on ion extraction. Concerning the principle of response, present plasticized PVC-based PhC works as a waveguide and a grating. Incident light was guided in the bulk of plasticized PVC and, then, guided light of a specific wavelength was diffracted by a periodic nanostructure. The guided and diffracted light intensity changes of PVC-based PhCs possessing various thicknesses were monitored at 580 nm; then, we found that the 0.35 mu m-thick PhC film exhibited the highest diffraction intensity. For the ion-sensing application, potassium-selective sensing elements involving potassium ionophore and lipophilic dye were dissolved in a plasticized PVC-based PhC, and the K+-selective response was successfully observed by monitoring the diffracted peak intensity change. The present 2D-PhC optical sensor exhibited a fast response within 5 s (95% response time) due to the use of thin film, and sensitivity was 20 times higher than that of a PVC plane-film optical sensor, due to efficient collection of diffracted light by employing a periodic nanostructure of the photonic crystal.