DETECTION OF PROTEIN CONCENTRATIONS USING A PH-STEP TITRATION METHOD

A stimulus-response method based on the application of a pH step is pr oposed for the detection of protein immobilized in a membrane on top o f an ion-sensitive field-effect transistor (ISFET). The ISFET response to a step-wise change in pH, applied at the interface between the mem brane and the surrounding solution, depends on the concentration of pr otein immobilized in the membrane because proton-dissociation reaction s of the protein cause a delayed diffusion of protons and hydroxyl ion s through the membrane. Our theoretical description shows that the del ay in ISFET response is linearly related to the concentration of prote in immobilized in the membrane. Experiments performed with lysozyme as a model protein show the feasibility of this detection principle. (C) 1997 Elsevier Science S.A.