In recent years, the demand for more economical medical equipments has been on the increase. One of them is biomedical sensor using MEMS and microfluidic technology. On emergency treatments, blood gas analysis of patient is very important thing to estimate his conditions. Our research is the development of blood gas analyzer, especially oxygen sensor. There are two research aims. One is achieving better operating performances such as accuracy and response time and the other is reducing manufacturing costs.
We make Clark-type oxygen sensors[1] with three-electrodes. For better redox reactions, face-to-face gold electrodes(working & counter electrodes), are fabricated on the silicon bulk-etched groove. Electrochemistry reaction efficiency of face-to-face electrodes are much higher than that of electrodes on the same plane. Ag/AgCl reference electrode is deposited on the corning 7740 Pyrex glass substrate covering silicon groove electrode substrate. PDMS sheet(2mm) is used for the bonding layer between silicon and Pyrex glass. Crucial part of fabrication is a gas permeable membrane. We make a thin PDMS membrane which is made for several steps. After several fabrication trials for easy sticking and thinner thickness we get a membrane with 8um uniform thickness. Thinner membrane thickness is fairly important for oxygen transportations from blood to sensor interior. Through this membrane, we get a fast reaction response which is quite essential to patient on emergency. Microchannels in which blood flows will be located under gas permeable membrane. The size of assembled device is 10mm X 10mm X 3mm and sensing area involving three electrodes and gas permeable membrane is 500um X 2mm X 500um. The small size means it is possible to make a portable device which medical doctors can easily carry to check patients on emergency moment. Therefore this research can be the beginning work for the future POCT(Point Of Care Testing) biosensor markets.
[1] Karagounis V, Liu L, Liu CC. A thick-film multiple component cathode three-electrode oxygen sensor. IEEE Trans Biomed Eng 1986;33(BME-2):108-12.
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