Simulations of the Potential Generation of an Enzyme-pH Fieldeffecttransistor (ENFET)

Abstract

In order to verify the chances of the enzyme-pH fieldeffecttransistor (ENFET) for the detection of urea in practical applications, in our group computer simulations have been carried out that scrutinized the influence of various parameters on the measurement signal. The described sensor uses a glutardialdehyde membrane containing the enzyme urease and an ISFET transducer, and is immersed in a buffer solution. If urea is added to the solution, it is metabolized to carbon dioxide and ammonia. The resulting pH-increase in the The program calculates a local distribution of substrate concentration and pH-value in the membrane. The influence of the above mentioned concentrations on the pH-value (which can be regarded as the measurement signal) is discussed. Above all these simulations show that for a working enzyme-pH sensor a well defined composition of the sample solution is essential. Therefore the ENFET works best in a flow-through-system, where all parameters can be kept constant, or together with a microtitration unit. membraneis measured by the ISFET. The simulation program is based on Michaelis-Mentenrelations and on adequatediffusion-reaction-equations for the concentrations of the enzyme, the substrate, and the reaction products, as well as the buffer capacity. Also the thickness of the membrane is taken into account.