Investigation of extracellular signal shapes recorded by planar metal micro electrodes and field-effect transistors

The extracellular recording from electrogenic cells is of growing interest in recent years. In principle, two different configurations for extracellular recording are primarily used. First, the metal microelectrode array (MEA) set-up, where metal microelectrodes are fabricated on a planar chip and the extracellular signals are amplified by an external circuitry. As a second approach, the signals can be recorded by planar, non-metallized field-effect transistors (FETs), which are mainly fabricated in silicon or recently in new type of materials like GaN/AlGaN. In this approach, the signals are pre-amplified by the FET on-chip. In the past there have been several attempts reported for a possible merge of the two approaches by using floating-gate or extended-gate transistor structures fabricated in a CMOS-like process. In recent years we fabricated, optimized and used all three configurations for extracellular recordings with different cell types. In this article we present extracellular signals recorded by these configurations and discuss the recorded shapes and amplitudes. It will be shown, that the correct design of the amplifier circuit is crucial for reliable signal shapes, which can be of electrophysiological interest.