CHARACTERIZATION OF PROTEINS BY MEANS OF THEIR BUFFER CAPACITY, MEASURED WITH AN ISFET-BASED COULOMETRIC SENSOR-ACTUATOR SYSTEM

Proteins form the specific selector in many biochemical sensors. A cha nge in one of the properties of such a protein has to be detected by a n appropriate transducer, which completes the biochemical sensor. One of these properties is the buffer capacity of a protein. If the bindin g of a substance to a protein can significantly change the proton bind ing, which accounts for the buffer capacity of proteins, the detection of this changed buffer capacity enables the construction of a new typ e of biosensor. It will be shown that the buffer capacity can be measu red with an ISFET-based sensor-actuator device. The alternating genera tion of protons and hydroxyl ions by alternating current coulometry at a porous noble metal actuator electrode causes an associated small pH perturbation, which is detected by the underlying pi-I-sensitive ISFE T. The amplitude of the measured signal is a function of the buffer ca pacity of the solute, in which proteins can be present (or these prote ins can be adsorbed in the porous actuator electrode of the device). A model describing the transfer function from the electrical input sign al of the actuator to the resulting chemical output, which is subseque ntly detected by the ISFET pH sensor, is presented. Preliminary result s of the measured buffer capacity of ribonuclease and lysozyme are pre sented.