F.J.B. Kremer

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.

Improved guanidinium ion-selectivity by novel calix[4]arene and calix[6]arene receptor molecules on CHEMFETs

Poly(vinyl chloride) membrane CHEMFETs incorporating a novel calix[4]arene derivative (1), novel calix[6]arene derivatives (3, 4, 5, 6 and 7), phosphate derivatives of p-tert-butylcalix[4]arene (2) or p-tert-butylcalix[6]arene (8) with variable amounts of hydrophobic anions [potassium tetrakis(4-chlorophenyl)borate (KTCTPB)] have been tested for their response to guanidinium ions in the presence of the interfering ions Na+, K+, NH4+ and Ca2+.The best guanidinium selectivity has been obtained for the CHEMFET based on the 1,3,5-triamide derivative of p-tert-butylcalix[6]arene (4), with dibutyl phthalate as solvent mediator, and 50 mol% KTCTPB with respect to the ionophore. The selectivity coefficients (log KpotGu,j) are the highest reported for guanidinium ions in a potentiometric sensor. The CHEMFETs show an almost ideal Nernstian response in the linear range (slope 58–60 mV decade–1).

Immobilization and activity of concanavalin A on tantalum pentoxide and silicon dioxide surfaces

The physical adsorption and chemical immobilization of Cancanavalin A (Con A) on semiconductor surfaces SiO2 and Ta2O5 are investigated with the help of radioactive-labelled Con A. It is shown that Con A easily forms multi-layered systems and that SiO2 has preference for the non-labelled protein. Surface coverage by the two methods is compared with respect to stability to mechanical stress and clearly shows the drawback of physical adsorption. In addition, the complexing abilities of Con A for mannose are investigated showing 50% activity compared to Con A in solution for monolayer systems, increasing to 75% for multi-layered systems.