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 μm-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.

Two-dimensional photonic crystals (2D-PCs) fabricated on a cyclo-olefin polymer (COP) film using a printable photonics technology based on nano-imprint lithography (NIL) were used for label-free biosensing of insulin under wet conditions. In general, 2D-PC-based biosensing involves a complicated dry-up procedure after biosensing reactions on the 2D-PCs to obtain a high sensitivity through the large difference in refractive index. Therefore, it can be difficult to achieve simple operation involving single-step analysis. Performance of the biosensing under wet conditions would simplify the operational procedure. For label-free biosensing of insulin under wet conditions, the Fresnel reflection intensity change was used instead of the wavelength shift, which is the commonly used sensing signal. By detecting changes in refractive index caused by specific interactions between the antigen and antibody as the Fresnel reflection intensity changes, physiologically important concentrations of insulin could be detected, even under wet conditions. These results suggest that low-cost printed 2D-PCs offer great potential for single-step label-free biosensing through the introduction of a sample solution.