Stretching of long DNA molecules in the microvortex induced by laser and ac electric field

A microvortex is generated around an infrared laser focus where an intense ac electric field is applied. The authors used this optoelectrostatic microvortex for stretching individual long DNAs. When λ-or T4-phage DNA molecules were introduced into the optoelectrostatic microvortex, they were stretched around the laser focus. In addition, especially for longer T4 DNA molecules, it was possible to keep it in stretching form for more than 30s. Using this method, length of DNA molecules can be measured without fixing to a substrate. This method can be applied to DNA molecules longer than about 10μm.