The electrical resistance in the narrow space between a cell and a solid substrate is unknown. It may differ from the resistance of bulk electrolyte due to electrical interactions of the surfaces involved. Here we present an approach to measure the extracellular resistance in the region of adhesion using transistor recording. We studied the adhesion of erythrocytes which were attached with poly-lysine to oxidized silicon. The cell membrane followed the surface profile of the chip at a distance of 10 nm as measured by fluorescence interference contrast microscopy. AC voltages of various frequencies were applied to the bath and the local voltage beneath a cell was recorded by a transistor. On the basis of a representative electrical circuit we determined a sheet resistance of 280 MOhm. Multiplication with the distance lead to a specific resistance of 280 Ohm cm, far above the specific resistance 74 Ohmcm of the bulk electrolyte.
Fig. 5: Erythrocytes on a chip with 96 transistors with most electrolyte removed from the chamber. The red blood cells are attached to the silicon dioxide with poly-lysine. The contacts to the drains point upwards. The common source is at the bottom. The lattice constant of the array is 3.6 µm. Scale bar 50 µm. Insert: Two erythrocytes in the gate region.
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