MODELING THE RESPONSE OF AN ENZYME POTENTIOMETRIC BIOSENSOR BASED ON pH-SENSITIVE FIELD-EFFECT TRANSISTORS FOR CREATININE DETERMINATION

The work presents a simulation of the kinetics of the responses of a potentiometric biosensor based on a differential pH-sensitive field-effect transistor (pH-FET) for the determination of creatinine using a bioselective element – the enzyme creatine deiminase. The modeling took into account such characteristics of the pH-FET as the threshold voltage and steepness of the transient I-V characteristic of the transistor, the composition and density of functional groups on the surface of the two-layer gate dielectric silicon oxide-nitride. The evolution of the change in the pH value of the solution near the transistor surface in response to the introduction of creatinine and the corresponding kinetics of the biosensor response are shown. The effect of enzyme immobilization in the PVA-SbQ photopolymer matrix on the enzyme concentration in the bioselective membrane is considered and the effect of the ionic strength of the buffer solution on the biosensor response is theoretically investigated. The obtained model results were compared with the experimental responses of the pH-FET of the creatinine biosensor in the range of substrate concentrations of 1-10 mM and their good correspondence was shown. The average modeling error was no more than 2% of the response value to the addition of 1 mM creatinine. It was shown that the calculated sensitivity values of the considered pH-FETs are in the range of 35-40 mV/pH for the working pH values of the solution, which corresponds to real sensor samples.