Neuron-silicon junction with voltage-gated ionic currents.

We recorded the signals of firing Retzius neurons from Hirudo medicinalis by field-effect transistors. The axon stump of dissociated cells was attached to an open gate coated with concanavalin A. We observed a new type of neuron-transistor coupling: the extracellular voltage transients beneath the neuron were dominated by a negative peak during the rising phase of the action potential with a weaker positive transient in the falling phase. The biphasic response was opposite to the signal of capacitive coupling. We simulated the junction on the basis of the Hodgkin-Huxley equations. We found that the negative transient corresponded to an inward flow of sodium and the positive response to an outward flow of potassium. The field-effect transistors are able to probe the local flow of ionic currents in a membrane which is hidden in the region of cell adhesion. They may become a novel tool in neuroscience.