Tatsuo Yoshinobu

Scanning laser beam semiconductor pH imaging sensor

Abstract We have constructed a two-dimensional (2-D) pH-imaging sensor that enables us to observe th H+ distribution produced by living cells. The pH-sensing principle is similar to that of thelight-addressable potentiometric sensor. The electrolyte-insulator-semiconductor (EIS) structure (electrolyteSi3N4SiO2Si) is illuminated by a focused (∼1 μm) and modulated (1–10 kHz) He—Ne laser bean from the backside of the semiconductor, and the a.c. photocurrent flowing through the EIS structure is measured. By scanning the laser beam, 2-D pH images can be obtained. By using this sensor, pH distributions of colonies of yeast (Saccharomyces cerevisiae) have been observed. The spatial resolution of this sensor could be improved by thinning the Si wafer.

Penicillin detection by means of field-effect based sensors: EnFET, capacitive EIS sensor or LAPS?

Abstract Three types of semiconductor field-effect penicillin sensors, enzyme field-effect transistors (EnFETs), capacitive electrolyte–insulator–semiconductor (EIS) sensors and light-addressable potentiometric sensors (LAPS) have been developed and tested for the penicillin detection. For all sensor types the enzyme penicillinase was adsorptively immobilised directly onto a pH-sensitive Ta 2 O 5 surface. Some basic parameters of these sensors (e.g. sensitivity, linear range, detection limit, response time, hysteresis and life time) are investigated and their performances with regard to the respective measurement set-up as well as the sensor configuration are compared.

High-resolution pH imaging sensor for microscopic observation of microorganisms

Abstract We have constructed a high-resolution pH imaging sensor, which enables one to observe the metabolic activity of microorganisms microscopically. A spatial resolution better than 10 μm was achieved by thinning the Si substrate to 20 μm, and by employing an infrared laser as an illumination source. Using a 100 kHz digital sampling technique for signal detection, a pH image of 128 × 128 pixels was measured within 15 min. The pH imaging sensor was integrated into a system for microscopic observation of incubated biological specimens such as microorganisms. Using the pH imaging sensor, Escherichia coli (E. coli) colonies incubated on agar medium for 8 h (visual size ∼0.2 mm diameter, number of cells ∼800) were detected. The observed pH distribution was in agreement with the result of simulation based on the production and diffusion of acidic ions.

Portable light-addressable potentiometric sensor (LAPS) for multisensor applications

Abstract A novel design of the light-addressable potentiometric sensor (LAPS) for realisation of a portable multisensor device is presented. Light sources and electronics including an oscillator, a multiplexer, a pre-amplifier and a high-pass filter are encapsulated in a pen-shaped case, on which the sensor plate is mounted. This sensor device is capable of measuring up to four different ion species by integrating different ion-selective materials on the sensing surface, each illuminated with an independent light source. The novel design of the sensor system is expected to make the measurement easier and to enlarge the field of practical applications.

Improvement of Spatial Resolution of a Laser-Scanning pH-Imaging Sensor

We investigated the spatial resolution of a laser-scanning semiconductor-based pH-imaging sensor both experimentally and theoretically. A spatial resolution better than 100 µ m was obtained by thinning the Si substrate to 100 µ m. The simulation results on the spatial resolution based on a carrier diffusion model agreed well with those obtained by experiment. From the simulation results, we also predicted the optimal choice of parameters of Si substrate (thickness, doping, etc.) for the pH-imaging sensor.

Heteroepitaxial growth of single crystalline 3C‐SiC on Si substrates by gas source molecular beam epitaxy

Heteroepitaxial growth of 3C‐SiC on Si substrates by gas source molecular beam epitaxy was investigated. Both Si(001) and Si(111) surfaces were carbonized using a C2H2 gas molecular beam to convert the surface region into single crystalline 3C‐SiC prior to crystal growth. The supply of C2H2 was started at 400 °C, and the substrate temperature was raised at a rate of 7 °C/min. An amorphous‐like layer was observed at 870 °C. Raising the temperature at a rate of 2 °C/min from 870 to 970 °C, a single crystalline 3C‐SiC layer was obtained. In the case of Si(001), increase of C2H2 supply resulted in improvement of crystallinity, because of a thin (∼50 A) 3C‐SiC layer formed at an early stage of carbonization, which prevented outdiffusion of Si atoms. The thickness of the 3C‐SiC layer did not increase for prolonged time of carbonization after formation of the thin layer. In the case of Si(111), the increase of C2H2 supply resulted in a thicker layer of 3C‐SiC with a rough surface, because the channels of Si outd...

Constant-Current-Mode LAPS (CLAPS) for the Detectionof Penicillin

A software feedback control system for the constant-current-mode operation of the light-addressable potentiometric sensor (LAPS) was developed. The constant-current-mode LAPS (CLAPS) is suitable for online monitoring and recording of changes in the pH value or the ion concentration. An enzyme LAPS was fabricated by adsorptive immobilization of penicillinase on the pH-sensitive layer of Ta2O5. This sensor was operated in the constant-current-mode and the detection limit for penicillin G was found to be at least as low as 100 µM.

Chemical-imaging sensor using enzyme

We have developed a new chemical-imaging sensor, which can visualize the two-dimensional distribution of a specific substance. This sensor uses an enzyme immobilized on the sensing surface of the pH-imaging sensor that we reported previously. As an example, a urea-imaging sensor has been fabricated using urease, and some two-dimensional patterns of urea distribution in agar visualized.

Observation of microorganism colonies using a scanning-laser-beam pH-sensing microscope

Abstract The extracellular pH-distribution of colonies of Saccharomyces cerevisiae (yeast) and Escherichia coli (E. coli) were observed using a newly-developed scanning-laser-beam pH-sensing microscope. Colonies were incubated either on top of agarose plates or between the pH-sensing surface and the agar. In the latter case, colony growth was observed in-situ. The colonies could be observed within a period as short as 8 h for E. coli. The pH-distribution profiles by the colonies were found to be very sharp, in agreement with simulation results.

AFM fabrication of oxide patterns and immobilization of biomolecules on Si surface

A novel method of protein patterning based on anodic oxidation of Si surface by atomic force microscope (AFM) is presented. An oxide pattern is drawn on the Si surface by applying d.c. voltage between the Au-coated AFM tip and the Si substrate. The oxide patterns can be used as a template for patterning of biomolecules. Protocols for both positive and negative patterning of protein were established.