Towards an Optimization of Fet-based Bio-sensors

Over the past 10 years, it has become possible to use the ISFET device as a cellular probe. The advantages of the ISFET, as opposed to conventional microelectrodes are (i) the possibility of measuring metabolic activity (via small pH changes in the culture media); (ii) the local amplification of the signal yielding less interference and noise and (iii) the possibility to multiplex transistor arrays. The latter is essential for designing large-scale sensor arrays. Electrical activity in cells has successfully been measured with ISFETS in the past (Fromherz et al, 1991, Offenhäusser et al, 1997) where a neuron sits on top of the non-metalized gate and induces an electrical signal into the ISFET channel. Metabolic activity has also been measured using ISFETS (Baumann et al, 1999) where the H+-sensitive layer of the ISFET, in proximity to a cell population, detects variations in cell metabolism via small (local) pH changes of the weakly buffered culture media.