Extracellular Potential Recordings by Means of a Field Effect Transistor Without Gate Metal, Called OSFET

The design and operation of a new semiconductor element, based upon the field effect principle is discussed. The device, which is called an OSFET, can be used as a measuring electrode for bioelectric activity. The OSFET consists of an MOS-transistor configuration, where the gate metal has been omitted and can be used directly in the extracellular fluid as an active probe. The operation of the OSFET is described by a physical-mathematical model, by means of which it is possible to explain the results of electrophysiological measurements. These results are compared with the results of a computer simulation, in which the Rosenfalck equation for extracellular potential distributions serves as an input for the OSFET model stated. A special electronic circuit is used to perform low impedance measurements in a simple way with the OSFET electrode. It appears that extracellular potentials measured with an OSFET-electrode have an extended frequency range, with respect to conventional potential measurements (0 ⩽< f ⩽< 45 K c/s).