CHARACTERISTICS AND APPLICATION OF THE ELECTROCHEMICAL LIGHT-ADDRESSABLE SENSOR-BASED ON SILICON WITH THE TA2O5 DIELECTRIC AND INTENDED FORRECORDING BIOCHEMICAL REACTIONS

Characteristics of a newly developed self-contained instrument, namely , a light-addressable potentiometric sensor, are reported. The sensor is intended for measuring solution pH and local pH variations, occurri ng in the regions of the sensor surface where enzymes, cells, and orga nelles are immobilized. The sensor can also be utilized for examining chemical sensitivity of silicon places, which are the sensing element of the instrument. The instrument consists of a functional block, whic h controls the mode of measurements, and a cuvette, which contains the sensing silicon plate with a pa-sensitive dielectric. The instrument provides for the measurement of current-voltage curves, i.e. the depen dences of the photocurrent generated an the bias potential for plates of the n-type; the automatic determination of the bias potential, whic h corresponds to the specified photocurrent, and the continuous photoc urrent recording at the specified bias potential. The instrument has b een used to study the chemical sensitivity of the silicon sensors that contain Ta2O5 as the pH-sensitive dielectric. The pH sensitivity obta ined is 45 mV per pH unit in the pH range from 4.01 to 7.5 (for measur ements conducted in solutions of a citrate buffer) and 55 mV per pH un it in the pH range from 7.5 to 8.9 (for measurements conducted in solu tions of a tris-HCl buffer). Initial reaction rates for glucose oxidat ion in the presence of glucose oxidase and for N-acetyl-L-tyrosine eth yl eater oxidation in the presence of alpha-chymotrypsin have been mea sured under the homogeneous conditions. The values of the Michaelis co nstant obtained agree well with the literature data. The instrument is treated as a basis for developing biosensor models of the potentiomet ric type.