Preparation of Cationic Liposomes & Transfection of Cells

Dissolve each lipid component (e.g., DOTAP/DOPE) in chloroform to a convenient working concentration (1-10mg/mL).
Aliquot the desired amount of each component into a glass vial using a glass syringe. More Information On Handling Organic Solutions Of Lipids.
Thoroughly mix the components in the glass vial.
Carefully evaporate the chloroform (with adequate ventilation) using a nitrogen or argon stream.
Place the lipid residue on a vacuum pump for 10-15 minutes to remove any residual organic solvent.
Remove the vial from the vacuum pump and immediately suspend in distilled water at twice the final lipid concentration.
Bath sonicate the lipid dispersion to clarity (2-5 min).
Add an equal volume of buffer (e.g., 308mM NaCl, 40mM Hepes, pH7.4), and sonicate further for 2 minutes.
Solution may be passed through a 0.22µm filter to sterilize.

Combine cationic lipid dispersion with DNA (1µg per 10µg lipid) in a suitable container.
Incubate lipid/DNA mixture for 5 min. at room temperature.
After 5 min., mixture is ready for transfection of cells.

Wash cell monolayers with HEPES-buffered saline two times.
Incubate cells with lipid/DNA mixture in HEPES-buffered saline (3 ml mixture per 100 mm culture dish) at 37°C for 90 min.
After the incubation period, either replace the medium or supplement as necessary.
Culture cells for desired period of time and harvest.

Common molar ratios of DOPE:cationic lipid are 3:1 and 1:1. In some cases, a lipid system composed entirely of cationic lipid has been used to transfect cells.
Buffer system cited is intended for in vitro use and does not suggest that this system may be suitable for in vivo use.