Techniques, systems and apparatus are disclosed for detecting impedance. In one aspect, a microelectrode sensing device includes a substrate and an array of microelectrode sensors formed on the substrate. Each sensor includes at least one conductive layer formed above the substrate and patterned to include a counter electrode and multiple sensing electrodes to detect an electrical signal in absence and presence of one or more target cells positioned on at least a portion of a surface of each sensing electrode. The sensing electrodes are spaced apart and arranged around the counter electrode to provide a spatially averaged value of the detected electrical signal.
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