Lipofectamine or Lipofectamine 2000 is a common transfection reagent, produced and sold by Invitrogen, used in molecular and cellular biology. It is used to introduce, that is transfect, siRNA or plasmid DNA into in vitro cell cultures by lipofection. Lipofectamine reagent contains lipid subunits that can form liposomes in a aquaeous environment, which entrapt the transfection materials, i.e. DNA plasmids. The DNA-containing liposomes can fuse with the plasma membrane of living cells and are engulfed, allowing nucleic acids to cross into the cytoplasm and contents to be available to the cell for replication or expression. This method of transfection was invented by Dr. Yongliang Chu at Life Technologies, Inc.