Professor Kazuaki Sawada’s work focuses on the development of biosensors that combine integrated circuit technology and sensor technology. Currently Prof. Sawada’s main project is working on a "bio image sensor", which he hopes to use to directly observe ion distribution and movement as visual images, in order to contribute to the development of brain science and disease diagnosis. There is growing excitement in the scientific community regarding the potential practical applications of this innovative sensor, which Prof. Sawada is striving to fulfill by establishing research associations and incorporated associations through industry-university.
Interview and report by Madoka Tainaka
Development of world's first sensor that can detect ion reactions
Today, the major types of image sensors for acquiring two-dimensional images by sensing are CCD (Charge-Coupled Device) and CMOS (Complementary metal-oxide-semiconductor). These semiconductor devices are mounted on digital cameras and smartphone cameras. They capture the amount of light as an amount of electric charge and process it after converting it to an electric signal and are widely used not only for cameras but also for measurement of magnetic fields and voltages. However, until now, there were no sensors that could directly capture the distribution and movement of ions, in the way that Prof. Sawada’s bio image sensor is now able to do.
"As a means for measuring ions, using litmus paper for measuring hydrogen ions is well established, but what sets our device apart is that it can measure the amount. This is the world’s first sensor that can directly observe the movement of ions," says Prof. Sawada.
The trigger for development dates back to Prof. Sawada’s fourth undergraduate year when he was a student at Toyohashi University of Technology. In response to a request from a company, he worked on the development of a hydrogen ion sensor through an industry-university collaboration that became his graduation thesis. However, the sensor didn’t achieve the desired performance and the research ended there. After that, Prof. Sawada worked for a time on material development, but after doing some research on image sensors at Shizuoka University more than ten years later, he decided to once again take on the challenge of becoming the first person to successfully image ion changes.
"As a mechanism, we read the movement of ions from the change in potential of a semiconductor (ISFET: Ion Sensitive Field Effect Transistor) by means of a sensitive membrane of ions placed on the surface of the semiconductor. It’s a little complicated, but at that time, depending on the concentration of hydrogen ions, a state called a "potential well" in quantum theory is formed on the semiconductor surface. To put it simply, the depth of the cup changes according to the concentration of ions. To measure the depth of the cup, we inject a lot of electric charge into it and measure the amount of charge that accumulates. We can then measure the electric charge by converting it into a voltage like a CCD or CMOS image sensor. In this way, we can read the ion concentration with a high level of sensitivity," explains Prof. Sawada.
In 1997, Prof. Sawada acquired a patent for this innovative method, and since then has continually strived to further develop and improve the bio image sensor.
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Dr. Kazuaki Sawada
Dr. Kazuaki Sawada received his B.A. and M.S. degrees in electrical and electronic engineering in 1986, 1988, respectively, and he received a Ph.D. degree in system and information engineering in 1991, all from Toyohashi University of Technology, Aichi, Japan.
From 1991 to 1998, he was a Research Associate in the Research Institute of Electronics, Shizuoka University, Shizuoka, Japan. Since 1998, he joined the Department of Electrical and Electronic Engineering, Toyohashi University of Technology, where he is now serving as a Full Professor.
Madoka Tainaka is a freelance editor, writer and interpreter. She graduated in Law from Chuo University, Japan. She served as a chief editor of “Nature Interface” magazine, a committee for the promotion of Information and Science Technology at MEXT (Ministry of Education, Culture, Sports, Science and Technology).