Micropipette system for sampling and injecting small volumes

We have developed a micropipette system that allows sampling of preset volu mes of liquids and injection of preset small amounts of liquids, using ther mal expansion of an oil phase in a micropipette, achieved by increasing or decreasing the current applied to heat the shaft of the micropipette. The s ystem has been tested to inject or collect volumes of about 20 nl, but smal ler and larger volumes are possible. The amount injected or collected for a given temperature step of the micropipette is largely independent of the p hysical 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 sam pled. (C) 1998 Elsevier Science B.V. All rights reserved.