Stretching yeast chromosomes using electroosmotic flow

In extended-fiber fluorescence in-situ hybridization (FISH), the location of a specific gene on a chromosome is determined by stretching the chromosome to a straight fiber and observing the binding of a fluorescence-labeled oligonucleotide under a microscope. In this paper, we propose and demonstrate the use of electroosmotic flow for the stretching of a chromosome. Electroosmosis is a liquid streaming which is induced by ion drag in the electrical double layer at a solid/liquid interface. Electroosmotic flow has large velocity shear near the wall, which is ideal for stretching chain-like polymers such as DNA, and the speed and the direction of the flow can be controlled by changing the magnitude and the polarity applied field. In the experiment, a yeast cell is immobilized onto a glass surface, its outer wall ruptured by the addition of an enzyme, and released DNA fibers as long as 200 μm are stretched by the method.