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Research paper : Development of high-sensitivity molecular adsorption detection sensors (M. Fujimaki et al.)−151−Synthesiology - English edition Vol.2 No.2 (2009) Si was suitable as a reflective film, and devised a method for forming the waveguide layer by thermal oxidation. Single-crystalline Si is suitable to obtain a uniform thermally grown SiO2 layer, which is scarcely damaged by the nanoprocessing. Therefore, we decided to use the SOQ substrate with a single-crystalline Si layer on a silica glass substrate. By forming the waveguide by thermal oxidation of the Si layer, we were able to develop a high-performance sensor as described above. By strategically combining several elemental technologies, we were able to obtain an integrated technology in the form of a high-performance sensor.6 Future issuesThere are two major issues in realizing the sensor. One is to demonstrate its function by detecting a target substance in actual measurement environment, that is, using samples of human origin such as blood and saliva that contain various foreign substances. Here, “selectivity” is important. The primary issue is to obtain high selectivity where other substances are separated from the target substance accurately. Therefore, to realize the actual outcome, it is important to develop a substance that can specifically capture a target substance originating from a particular disease. Also, we would like to aim for high selectivity by using the detection method using color based on what we learned through this study and by developing dyes that can specifically colorize target samples. The second issue is production costs. Since it is for medical use, it is desirable to keep the cost of the sensing plate to about 100 yen at most. We hope this can be achieved by incorporating the integration technology and mass-producing the product.7 ConclusionThrough this sensor development, we were able to obtain detection sensitivity that can sufficiently meet the demand of practical use. We were also able to show the possibility of reducing the effects of foreign substances and temperature change that were major issues in the conventional sensors. The developed sensing plate has high physical and chemical stability. Moreover, though it was not mentioned in the paper, by using the SiO2 waveguide, it is possible to use silane coupling for surface modification in molecule detection. Silane coupling is a very strong, simple, and low-cost surface modification method. Also, our device is suitable for downsizing. Currently, we are working on a desktop device about the size of a college dictionary. We obtained good results for the factors assumed at the start of the development. In the future, we would like to cooperate with the researchers of fields that require such sensors, and promote collaboration with medical institutions and researchers of different fields such as chemistry and biosciences. We would also like to continue our research to realize a sensor that can serve the medical field.AcknowledgementWe express our gratitude to Nobuko Fukuda, researcher of Biophotonics Group, Photonics Research Institute, Professor Yoshimichi Ohki and the students of the Ohki Lab, Faculty of Science and Engineering, Waseda University, who helped us with the waveguide mode measurement experiment; Dr. Tetsuro Komatsubara of the University of Tsukuba Tandem Accelerator Complex, who helped us with the ion irradiation experiment; Xiaomin Wang of Center for Applied Near-Field Optics Research and Dr. Carsten Rockstuhl of Friedrich Schiller University Jena, who helped us with the simulation; and all the people involved. The authors would also like to thank the Advanced Functional Materials Research Center of Shin-Etsu Chemical Co., Ltd. for supplying the SOQ substrate.TerminologyFig.17 Flow of the R&D.Breakthrough: Utilize change in optical absorption. ・ Sensitivity 1000 times or higher ・ Reduction of effects of foreign substances ・ Reduction of effects of temperature ・ Simplification of optical system was realized. WaveguidemodeTargetmoleculeHigh sensitivity, high stability,high reliabilityFormation of nanopores with highaspect ratio ・ Sensitivity improvement of one- digit or moreSubstrate material: SOQ substrate is used.Waveguide: Single-crystalline Si layer is thermally oxidized. ・ Realized high sensitivity and high stability ・ Reduced roughness of surface during nanopore formationReflective film material: Si is used. ・ Good adhesiveness with glass ・ Physically and chemically stable ・ Good sensitivity ・ Good processing capacitySingle-crystalline Sireflective filmSiO2 substrateMonolithic sensing plate with nanoporesReflective layerWaveguide mode: When light is transmitted by total reflection within a limited medium, the angles of reflection are limited and become intermittent. The distribution of light intensity within the medium forms “nodes” where the light intensity is mutually strengthened and weakened by resonance. The state where the light is propagating while maintaining such light intensity distribution is called the waveguide mode. One example is the propagation mode in an optical fiber.Surface plasmon: Plasmon is a phenomenon in which the free electrons in metal vibrate as a group. In general, light does not couple with plasmon, but an Term 1. Term 2.

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