NOVEL BIOSENSOR SYSTEMS FOR CLINICAL AND FOOD ANALYSIS USING MICRO DEVICES

Abstract

The amorphous silicon ion sensitive field effect transistor (a-ISFET) made by radio frequency plasma discharge was used as a pH-sensitive device. The size of the channel of the a-ISFET is 10 um long and 500 um wide. The pH sensitive layer was silicon oxide evaporated over the amorphous silicon nitride layer. The pH sensitivity was about 46 mV/pH at 18°C in the range pH 5-10. The response times of this device to pH change are very rapid, being less than 30 sec to reach a steady state value. The fish freshness sensor was constructed by using an immobilized xantine oxidase membrane and a-ISFET. Hypoxantine was detected in the range 0.02-0.1mM. Micro-biosensors for glucose and glutamate were constructed by using silicon fabrication technology. A linear relationship was observed between the glucose concentration in the range from 0.1 to 10 mg aı-!, and the decrease in current. Glutamate was determined in the range from 5 to 50 mM. The microoxygen electrode consists of two gold electrodes and agarose gel containing electrolyte covered with a gas permeable membrane. A negative photoresist was used as the gas permeable membrane which was directly cast onto the gel and submitted to photochemical reaction. A 90% response time of the micro-oxygen electrode took approximately 3 minutes. A linear relationship was obtained between the response of the micro-oxygen electrode and that of a conventional Galvanic oxygen electrode.