Micro-biosensors for Clinical and Food Analyses

Abstract

Micro-biosensors for glucose and fish freshness were constructed by using silicon fabrication technology. A micro-H₂O₂ electrode was used to make a micro-glucose sensor. Glucose oxidase was immobilized on an organic membrane, prepared by vapor deposition of γ-aminopropyltriethoxysilane (γ-APTES) and glutaraldehyde, and used for glucose determination in the range from 0.1 to 10 mg dl^-1. The micro-oxygen 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 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 convinient Galvanic oxygen electrode. This sensor responsed almost linearly for glucose concentrations between 0.2 and 2 mM. The amorphous silicon ion sernsitive 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 μm long and 500 μm 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 xanthine oxidase membrane and a-ISFET. Hypoxanthine was detected in the range 0.02–0.1 mM.