Cationic lipidoids have potential applications in the field of gene delivery due to their unique properties.We use combinatorial chemistry to synthesize libraries of thioether lipids that are composed of cationic head groups and hydrophobic tails.High throughput screening of these biomimetic lipid libraries has demonstrated their ability to deliver plasmid DNA and siRNA into the cells [1,2,3].We use these libraries to screen for new lipids that have high transfection efficiency combined with low toxicity in several different cell lines.The goal of this research is to develop a screening and optimization platform for the development of more efficient and cost-effective transfeetion reagents,suitable for a variety of cells,including cells that are difficult to transfect.