Combinatorial synthesis of lipidoids for DNA delivery. (A) Alkyl-acrylamide, alkyl-acrylate, alkyl-epoxide, and amine molecules used for the library synthesis; (B) Chemical structures of the selected lipidoids with high DNA delivery efficiency. Lipidoids are named as follows: (carbon numbers of tail) (acrylate, acrylamide, or epoxide)-(amine number)