A probe array comprises a substrate having an array of pillar probes 44, i.e. electrodes, extending in a direction orthogonal to the plane of the substrate and having a first cross-sectional area. Each probe is disposed on a pedestal 45 formed on the substrate where each pedestal has a second cross-sectional area greater than the first cross-sectional area and forms a platform from which the pillar probe extends. A plurality of channels 47 are formed between the pedestals, the channels each having a width less than the spacing between the pillar probes. The channels ensure that a supply of critical fluids can be delivered to an underside of a cellular sample into which the pillar probes penetrate. In embodiments, the pedestals and pillars may be arranged in a two-dimensional grid area.
