J. Kruise

Detection of protein concentrations using a pH-step titration method

A stimulus-response method based on the application of a pH step is proposed for the detection of protein immobilized in a membrane on top of an ion-sensitive field-effect transistor (ISFET). The ISFET response to a step-wise change in pH, applied at the interface between the membrane and the surrounding solution, depends on the concentration of protein immobilized in the membrane because proton-dissociation reactions of the protein cause a delayed diffusion of protons and hydroxyl ions through the membrane. Our theoretical description shows that the delay in ISFET response is linearly related to the concentration of protein immobilized in the membrane. Experiments performed with lysozyme as a model protein show the feasibility of this detection principle.

Detection of charged proteins by means of impedance measurements

The electrical resistance of a membrane containing charged proteins is a function of both concentration and mobility of the electrolyte ions present in the membrane, and thus it depends on the Donnan effect. We were able to determine the resistance of such a membrane deposited on an ISFET, by means of a simple a.c. impedance measurement. As an example a membrane containing cross-linked lysozyme was used. We found the membrane resistance to be inversely proportional to the fixed charge density, in good agreement with the theoretical description based on the Donnan theory.

Chemical sensors for in vivo monitoring : fundamental approaches and promises of available technologies

In order to promote the development and application of chemical sensors for in vivo monitoring. a series of workshops has been organized by the European Community Concerted Action on “Chemical Sensors for Monitoring”. The third Workshop of this Concerted Action was held on 6–9 March 1990 at the University of Twente in Enschede, the Netherlands. After the lirst two orkshops, in which the clinical aspecfs (Lyon, 8–10 March 1989) and the device strategies (Florence, 12–15 November 1989) were discussed. In this workshop the main topic was the technological aspects of microsensors to be used for hyirnsensing. A report of the third workshop is presented, which is entitled: “In yirp sensing: fundamental approaches and potential promises 01 available technologies”.