DETERMINATION OF THE INFLUENCE OF TEMPERATURE AND UV TREATMENT ON THE CHARACTERISTICS OF DIFFERENTIAL ISFET ELECTRODES

Abstract

The work is devoted to the study of the influence of temperature, UV radiation and a number of additional chemical treatments of crystals of ion-selective field- effect transistors in the electrode assembly in order to carry out appropriate types of chemical-technological treatments of the crystal surface and improve its ability to immobilize biosensitive elements. The influence of ultraviolet treatment on the characteristics of differential pH-FET (threshold voltage and channel current difference) was studied and the long-term effect of such influence was determined. Irreversible in time and significant symmetrical shift of the threshold voltages of both transistors on the crystal in the direction of a decrease in their absolute value from –(1.5–1.6) V to –0.6 V was revealed. It was shown that most electrodes with asymmetric I–V characteristics in the initial state become almost symmetrical after UV treatment, which makes it possible to use them as differential electrodes. It has been established that the relaxation process after UV irradiation is 90% complete within the first 10 days. Limits of permissible heating temperatures of ISFET electrodes of the described design, which do not lead to their failure, have been established. It is shown that the maximum safe heating temperature of the assembled electrodes is no more than 100 ºС when kept for 2 hours, and when heated to a temperature of 130 ºС for 2 hours, the symmetry of the current-voltage characteristics was violated in about 10% of the electrodes, and a drift of the current difference occurred, which lasted for the next 2 days after the temperature treatment. The influence of a number of additional chemical and technological treatments (with the help of a chromium mixture, a «piranha» solution and silanization of the nitride-silicon surface of the crystals) on the parameters of ISFET electrodes was studied. Protocols for effective cleaning and silanization of sensitive surfaces of transistors have been developed. A study on the modification of ISFET electrodes with silver and gold nanoparticles in order to improve their ability to immobilize biological reagents was carried out. It is shown that the use of gold nanoparticles in the composition of the enzyme membrane leads to a significant increase in the operating responses of enzyme biosensors.