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Nickel electrodes chemically modified with an interfacial layer of nickel ferrocyanide are shown to be of analytical utility for simultaneously sensing sodium and potassium ions in aqueous solutions, human whole blood serum, and human whole blood. By controlling the charge-transfer characteristics of this versatile interface, interfering blood proteins and potential interferences associated with other alkali cations can be avoided. A solid-state model which explains the excellent simultaneous selectivity and sensitivity of the nickel ferricyanide interface is proposed.

A noninvasive biomagnetic sensor system that uses magnetic toroids for both neural stimulation and detection is described. It is shown that analytical signals obtained by direct magnetic detection (no signal averaging) compare favorably with electrical monitoring and that dose-response curves for local anesthetics correlate well between the two methods. Neural lifetimes are significantly extended when the noninvasive biomagnetic sensing system is used.

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We report the generation of action potentials in crayfish neurons by magnetic pulses for analytical purposes. A copper wire toroid, containing a ferrite core, was placed around the nerve bundle, and square wave current pulses were sent through the wire to generate a magnetic field. The magnetic field generated an action potential in the neuron that was detected downfield by a pickup microelectrode. The biosensor was used to detect local anesthetics by monitoring the time necessary for complete blockage of the action potential. Techniques for improving the efficiency and lifetimes of neural biosensors are discussed.