Chemical imaging sensor for observation of microscopic pH distribution

Motoi Nakao; Satoshi Nomura; Shuji Takamatsu; Katsuhiko Tomita; Tatsuo Yoshinobu; Hiroshi Iwasaki

doi:10.1117/12.323922

8 September 1998 Chemical imaging sensor for observation of microscopic pH distribution

Motoi Nakao, Satoshi Nomura, Shuji Takamatsu, Katsuhiko Tomita, Tatsuo Yoshinobu, Hiroshi Iwasaki

Proceedings Volume 3514, Micromachined Devices and Components IV; (1998) https://doi.org/10.1117/12.323922
Event: Micromachining and Microfabrication, 1998, Santa Clara, CA, United States

Abstract

A novel chemical imaging sensor has been developed using a Si semiconductor. The sensor (Si₃N₄/SiO₂Si) is in contact with the electrolyte solution that serves as an objective sample. The backside of the Si substrate is illuminated by a modulated laser beam. The AC photocurrent flows through the electrolyte-insulator-semiconductor. The intensity of the photocurrent depends on the electrolyte solution pH value on only the illuminated region. A 2D pH distribution can be obtained by scanning the focused laser beam. The sensor visualizes the pH distribution in the gel solution induced by ion exchange resin and microorganisms. The spatial resolution of this sensor is restricted by the Si substrate thickness as well as the laser beam spot size. A practical sensor with a spatial resolution better than 5 micrometers was fabricated using a SOI wafer instead of Si wafer, and anisotropic chemical etching instead of mechanical polishing. Such a high spatial resolution makes it possible to detect the microscopic pH distribution in solution. A reduction of spatial resolution due to the lateral spread of the depletion layer was estimated at approximately 80 nm in the present sensor system. The pH resolution of this sensor was also estimated to be 0.01 pH.

Citation Download Citation

Motoi Nakao, Satoshi Nomura, Shuji Takamatsu, Katsuhiko Tomita, Tatsuo Yoshinobu, and Hiroshi Iwasaki "Chemical imaging sensor for observation of microscopic pH distribution", Proc. SPIE 3514, Micromachined Devices and Components IV, (8 September 1998); https://doi.org/10.1117/12.323922

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