The invention relates to a method for carrying out measurements on cells located in a liquid environment wherein each cell is positioned with an underside of its membrane on a surface, the surface having at least one channel running through it, in which, to aspirate the cell to the surface, a pressure differential is established and the cell, in addition, is electrically scanned via at least one electrode.
The invention further relates to a device for carrying out electrical measurements on cells located in a liquid environment, comprising a substrate which has a channel running through it, above which a cell can be positioned with an underside of its membrane on a surface of the substrate, means being provided to generate a pressure differential along the channel, and a first electrode being provided for electrical scanning of the cell.
It is known to employ so-called microelectrode arrays for the study of biological cells, the microelectrode arrays being used e.g. to stimulate the cells or to tap potentials. The studies can be carried out in a biological environment or alternatively in an artificial environment. The arrays to this end comprise, in a matrix, a plurality of microelectrodes whose dimensions are of about the order of magnitude of the cells, i.e. in a range from a few μm up to a few tens of μm. A microelectrode array of this general type is disclosed e.g. by WO 97/05922.
In conventional microelectrode arrays it is more or less a matter of having to rely on chance as to whether one cell or some other cell will or will not settle on a specific electrode. In practice, the cells will generally only partially cover an electrode when settling on it, so that stimulation of the cell or tapping of a cell potential is limited to this sub-area. Moreover, the cells are only loosely seated on the electrodes. This may lead to problems with regard to the sealing resistance with respect to the reference electrode. Alternatively, cells may come to lie outside the range of an electrode, so that the measurement will not pick them up.
In the case of the microelectrode array disclosed by DE 197 12 309 A1 these drawbacks are avoided by the cells being collected in micro-cuvettes at whose bottom an electrode is located. The electrode is provided with a central channel in which a negative pressure can be produced via suitable connecting channels which run below the electrodes. Thus it is possible for individual cells to be drawn to the electrodes in a controlled manner and to be affixed to the electrodes with a certain contact pressure. Measurements can then be carried out on the electrodes, but only from outside them.
From another art, the so-called Patch Clamp technique, it is known to aspirate cells at a pipette using negative pressure (cf. US-Z “NATURE”, vol. 260, pp. 799–801, 1976). The Patch Clamp technique, however, requires a controlled approach of the pipette to an individual cell. With the Patch Clamp technique the cells to be contacted are not moved, since as a rule they are adhering to a substrate. Conventional contacting of cells using Patch Clamp pipettes has a drawback, however, that the number of cells that can be contacted simultaneously is extremely limited, since for reasons of space it is not possible to introduce arbitrarily many pipettes into the culture chamber.
On the other hand, the Patch Clamp technique has the advantage, compared with the above-described technique which only permits measurements from the outside of the cell, that the cell interior can be included in the measurement.
In the Patch Clamp technique as employed conventionally, using individual pipettes, this is achieved, under observation by microscope, by a fragile glass pipette being moved, by means of a micromanipulator, to a single cell adhering to a substrate and the membrane being cautiously aspirated to the pipette mouth. There is therefore direct contact between glass surface and membrane surface. By this means, a membrane patch is sealed and electrically insulated from the surrounding fluid. This insulation is also referred to as a gigaseal. The transition from this “cell-attached configuration” to the so-called “whole cell configuration” is achieved by further aspiration of the sealed membrane. This is done in such a way that the membrane section below the pipette is perforated. This results in hydraulically and electrically sealed access via the pipette mouth to the cell interior. The remaining cell membrane is thus electrically accessible in its entirety (so-called “whole cell patch”). Using this conventional technique does, however, require a considerable level of experience and very sensitive touch. A plurality of cells can only be processed sequentially. This method is therefore unsuitable for large-scale studies as would be required e.g. in the field of pharmaceutical screening, substance screening and the like.