Frequency dependent signal transfer in neuron transistors

Nerve cells are attached to open, metal-free gates of field-effect transistors submersed in electrolyte. The intracellular voltage is modulated by small ac signals from 0.1 Hz to 5000 Hz using a patch-clamp technique. The source-drain current is affected in amplitude and phase through a modulation of the extracellular voltage in the cleft between transistor and cell. The ac-signal transfer is evaluated on the basis of linear response theory. We use the model of a planar two-dimensional cable which consists of the core of an electrolyte sandwiched between the coats of a cell membrane and silicon dioxide of the transistor surface. Comparing experiment and model we obtain the resistances of core and coat, i.e., of the seal of cell and surface and of the attached membrane. The resistance of the membrane varies in different junctions. It may be lowered by two orders of magnitude as compared with the free membrane. This drop of the membrane resistance correlates with an enhancement of the seal resistance, i.e., with closer adhesion. The linear ac-transfer functions are used to compute the signal transfer of an action potential. The computed response is in good agreement with the observations of excited nerve cells on transistors.