Shoma Aki

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 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.

Origin of the Optical Response of a Dye-doped Plasticized Poly(vinyl chloride)-based Photonic Crystal Ion Sensor

We investigated the origin of the optical responses of a two-dimensional photonic crystal (2D-PhC) optode membrane ion sensor based on plasticized poly(vinyl chloride) (PVC) containing lipophilic dye. We previously developed a highly sensitive potassium ion sensor. However, the contributions of various factors to the sensors optical response could not be distinguished. Here, we synthesized a lipophilic dye with spectral changes that do not overlap with those of propagated light in the PhC. Using this synthesized dye excluded the contribution of light absorption by the dye to the peak intensity change of the ion sensor. In refractive index standard solutions, the bulk refractive index change upon ion extraction contributed negligibly. The contribution of diffracted light scattering by optical transparency change of the plasticized PVC upon ion extraction accounted for approximately 45% of the ion sensors total response. These findings are important for the development of highly sensitive plasticized PVC-based 2D-PhC ion sensors.

Development of optical biosensor based on photonic crystal made of TiO2 using liquid phase deposition

We developed TiO2-based photonic crystal (PhC) for highly-sensitive optical biosensing application. The optical characteristics of PhC depend on refractive index of base material and surroundings. Hence, highly-sensitive optical biosensing application is expected by using high refractive index base material. By using TiO2-based PhC biosensor, detection of antigen-antibody reaction was successfully achieved.

Polymer-based Photonic Crystal Cavity Sensor for Optical Detection in the Visible Wavelength Region.

In this study, a polymer-based two-dimensional photonic crystal (PhC) cavity for visible-light-based optical-sensing applications was designed and fabricated for the first time. The PhC cavity configuration was designed to operate at 650 nm, and fabricated with a polymer (resist) on a silicon substrate using electron-beam lithography. For investigating sensing applications based on shifting of condition exhibiting a photonic bandgap (PBG), the polymer monolayer deposition (layer-by-layer method) was monitored as the light-intensity change at the cavity position. Consequently, the monolayer-level detection of polyions was achieved.

Design and Fabrication of a Visible-Light-Compatible, Polymer-Based Photonic Crystal Resonator and Waveguide for Sensing Applications

In this paper, we have proposed a polymer-based photonic crystal (PhC) resonator, with multiple sizes of cavities, and a waveguide to be used as highly sensitive optical sensor components. Properties of the proposed PhC were simulated by the finite-difference time-domain method, and the polymer-based PhC resonator and waveguide were fabricated on a photoresist (polymer) by electron beam lithography, which was prepared on an Au-layer-deposited Si substrate. We detected the resonant light that penetrated through the waveguide and was trapped in the PhC resonator. Optical characteristics of the fabricated PhC were evaluated by detecting the polymer layer deposition process by using the layer-by-layer (LbL) method to deposit polymer layers. As a result, by using an optimized design of a polymer-based PhC resonator with a long cavity (equivalent to a defect of three holes), the PhC structure changes caused by LbL deposition lead to changes in resonant light wavelength (peak shift: 5.26 nm/layer). Therefore, we suggest that a PhC resonator and a waveguide is applicable as an optical sensor.