Katsuhiko Tomita

Novel CCD-based pH imaging sensor

We propose and demonstrate a novel pH imaging sensor based on the Charge Coupled Device (CCD) technology. This device consists of pH sensing parts, which sense pH value and transform a pH value to electric charges, and conventional CCD parts, which transfer the electric charges to read out circuit. A thin Si/sub 3/N/sub 4/ film which acts as the hydrogen ion-sensitive membrane was used in the pH sensing film. The prototype devices were fabricated and was confirmed the device operation using pH equivalent voltages. It was found that the output signal from the imaging sensor was lineally changed from pH 0 to 14 and successfully observed a pH image on a black and white TV monitor.

Real-Time Imaging of Microscopic pH Distribution with a Two-Dimensional pH-Imaging Apparatus.

Real-time two-dimensional pH imaging has become possible with the development of a new type of potentiometry, by which the pH distribution can be visualized as pH images with submillimeter spatial resolution. The measurement time for one image is short enough for practical use. The transient change of pH distribution generated by the protons released from a single cation-exchange resin was observed and visualized as the pH images. From the pH images, the evaluation of the resin performance was also carried out.

Application of Chemical Imaging Sensor to Electro Generated pH Distribution

The scanning-laser-beam chemical imaging sensor was applied for the observation of electrogenerated pH distribution on a mesoscopic scale. Electrolysis was carried out in potassium chloride solution and the resulting pH distribution was imaged with a 0.2 mm spatial resolution. As a result, the generation of the pH distribution and its expansion to the bulk region were clearly imaged. By examining the pH image, it was also possible to obtain the pH values in the pH-distributed regions separately from those in the bulk region.

Chemical imaging sensor for observation of microscopic pH distribution

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.