F. Felderer and P.Fromherz
We report on a proof-of-principle experiment for the direct interfacing of transistors with intact brain tissue. A transistor needle chip (TNC) with a TiO2 surface is fabricated from a silicon-on-insulator wafer and impaled into an acute brain slice from the hippocampus of the rat. While stimulating the Schaffer collateral, a local field potential is recorded in stratum radiatum of the CA1 region with field-effect transistors in the central part of the slice where the tissue is not damaged by the cutting process. After the impalement, the signal amplitudes are small. Within an hour, they increase to stable levels around -2 mV as they are recorded with conventional micropipette electrodes. The recovery indicates that the tissue is able to adapt to the impaled chip. Upon repeated impalements at the same position, the large signals are observed without delay. A profile of the transistor signals across the slice is due to the boundary conditions of a brain slice with both surfaces held near ground potential. The experiments with the TNC prototype are a basis for the development of silicon needle chips with a large multi-transistor array (MTA) for applications in brain-computer interfacing.
Figure 1. Electronmicrograph of a transistor needle chip (TNC). The picture shows the thin needle with four transistors and a portion of the thick contact plate with one of the metalized bond pads. The insert shows the shape of the needle tip. lines mark the surfaces of the slice.
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