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Neuron-Silicon Junction with Voltage-Gated Ionic Currents.
Richard Schätzthauer and Peter Fromherz, Eur.J.Neurosci. 10 (1998) 1956-1962.
Abstract. 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.

Fig. 2a: Experimental neuron-silicon junction. Top: Micrograph with the axon stump of Retzius cells on a linear array of transistors. The open gates are close to the terminals of the dark stripes (drains) at a distance of about 5 µm . The recording site is indicated by a cross. Below: Intracellular voltage VM(t) and extracellular voltage in the junction VJ(t) as a function of time (Zero time at the maximum of the action potential.) Stimulation current 1.6nA. The number of averaged signals N is indicated. C1-type junction. Biphasic response with a leading negative transient in the rising phase of the action potential and a positive transient in the falling phase.