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We have developed a micropipette system that allows sampling of preset volumes of liquids and injection of preset small amounts of liquids, using thermal expansion of an oil phase in a micropipette, achieved by increasing or decreasing the current applied to heat the shaft of the micropipette. The system has been tested to inject or collect volumes of about 20 nl, but smaller and larger volumes are possible. The amount injected or collected for a given temperature step of the micropipette is largely independent of the physical properties, e.g. of viscosity, into which the sample is injected or from which it is collected. The pipette tip is not measurably heated when heating the shaft for injection or collection, thus avoiding damage of the biological material into which the injection occurs or from which it is sampled. |
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