Abstract: A CHEMFET (chemically modified field-effect transistor) for detecting Cd2+ in solution was obtained by chemically modifying an ISFET with NNN'N'-tetrabutyl-3,6-dioxaoctanedithioamide in a cyanopropyl-modified polysiloxane membrane. The CHEMFET had a Nernstian response (30 mV per decade) to a change in Cd2+ activity when tested in the presence of 100 mM Ca(NO3)2. There was also a Nernstian response with K, Cu and Pb as interfering salts; selectivity coefficient are given. The CHEMFET also gave a Nernstian response to change in Cd2+ activity when used in a flow injection system without polymeric encapsulation of the CHEMFET. An ion-selective field-effect transistor (ISFET) is chemical modified with a photopolymerizable and cyanopropyl modified polysiloxane containing N,N,N',N'-tetrabutyl-3,6-dioxaoctanedithioamide as Cd2+ ionophore. This CHEMFET (chem. modified FET) has a Nernstian response (30 mV/decade) to a change of cadmium activity in aqueous solutions Selectivity coefficients of the CHEMFET towards potassium, calcium, copper, and lead are given. Preliminary results of the CHEMFET in a flow injection analysis cell without wire bonding and polymeric encapsulation are presented.

Abstract: In comparison with selective receptors (and sensors) for cationic species, work on the selective complexation and detection of anions is of more recent date. There are three important components for a sensor, a transducer element, a membrane material that separates the transducer element and the aqueous solution, and the receptor molecule that introduces the selectivity. This review dears with potentiometric transduction elements that convert membrane potentials into a signal. The structure and properties of membrane materials is discussed. The nature of the anion receptor ultimately determines the selectivity. Both coordination chemistry and hydrogen bonding have been used to design anion receptor molecules. The integration of all three elements by covalent linkage of all elements in durable sensorsystem concludes the review.

Abstract: The ISFET were made as previously reported by Van der Wal et al. (Ibid., 1990, 231, 41), but with modifications for use in flow cells, and two of the devices were mounted in close proximity in a flow-through cell made from Perspex. A hydrogel was applied to the gate oxide of the ISFET and Na+-, K+- and Pb2+-sensitive membranes were prepared. Measurements were made with a K+-sensitive ISFET in a fixed excess of Na+ (Na+-sensitive ISFET as reference) and with a Pb2+-sensitive ISFET in a fixed excess of K+ (K+-sensitive ISFET as reference). In both instances the differential signal gave a Nerstian response.