Micro-injection by thermal expansion

A micropipette (diameter 5 to 20 micron) sealed near the orifice to provide a small closed reservoir is described. The reservoir is filled with oil and can be heated with a tiny electric resistance wire loop. Thermal expansion and contraction of the oil in the reservoir allows liquid to be expelled or aspirated. The flow of the liquid can be controlled accurately by varying electric current. Detailed instructions are given for fabricating the micropipette and the heating assembly. A plan for a handy micropipette puller is given. The technique has proved to be valuable in nuclear transplantation and injection of fluid volumes between 1 and 100 picoliters into Drosophila eggs.