Anal. Chem. 1981, 53, 1983-1986
1983
Field Effect Transistors Sensitive to Sodium and Ammonium Ions Urs Oesch, Steve Caras, and JIfi Janata” Depatfment of Bioengineering, University of Utah, Salt Lake City, Utah 84112
New Ion-selective field effect transistors (ISFET) for Na+ and NH4+ are presented. They are based on well-estalblished Ion-selectlve solvent polymeric membranes containlrig synthetlc neutral carrier ETH 227 and monactln/nonactin, respectively. Thelr selectlvlty and sensitivlty are coincident to the corresponding potentiometric Ion-selective electrodes. Their drifts are 51 mV/h which is typical for the present state of chemically serisltlve field effect transistors. Response times are determllned around 15 ms and found to be intrinslc for such membrane systems.
The theory of ion-sensitive field effect transistors (ISFET) has been reviewed recently and the mode of operation of these devices has been compared with conventional ion-selective electrodes (ISE) ((1,2). The principal advantages of ISFETs are their small size, the in situ impedance transformation, the ability for temperature and noise compensation, andl the possibility of manufacturing small, combined multisensors including the required reference electrode (1,2). Solvent casting has been proven to be suitable for application of liquid polymeric membranes to manufacture ISFETs. With this procedure ISFETs sensitive to calcium, potassium, and hydrogen ions (3)and various halide ions (4) have been developed. In this paper, the preparation and feasibility study of a Na’ ISFET and a NH4+ ISFET are described, using highly improved solvent polymeric membranes based on Na+ ionophore ETH 227, and the macrotetrolide antibiotic nonactin/manactin, respectively. These membranes have already found applications in ISEs (5, 6) and Na+ microelectrodes (7, 8). EXPERIMENTAL SECTION Chemical/Reagents. Cyclohexanone (analytical grade, freshly distilled), potassium chloride (analytical grade,
