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.

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.

Biomagnetic neurosensors based on magnetic stimulation and magnetic detection of neural events depend critically upon the effective matching of the magnetic transducers and the neural tissue employed. Although the properties of wire-wrapped ferrite core transducers can be predicted from electromagnetic fundamentals, meaningful analytical measurements using real nerves as molecular recognition elements require additional calibration and optimization steps in order to achieve good system response and lifetimes. This note provides some design guidelines and experimental test procedures to enable potential users to employ biomagnetic neurosensors in other laboratories.

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