Gene transfection means the delivery and introduction of biologically functional nucleic acid into a cell, by which the nucleic acid retains its function within the cell. The nucleic acid includes DNA (plasmid and linear double strand DNA), antisense oligonucleotide and RNAi (RNA interference). Gene transfection has been widely applied in genomic function studies (gene regulation, gene function, signal transduction and drug screen studies) and gene therapy studies.

Gene carrier is needed for introducing nucleic acid into cells. Both viral and non-viral gene carrier have been used in gene transfer. Viral vectors have highest efficiency, but the safety of virus, the high expense and the complicated procedure in viral vector preparation hampers its applicability. On the other hand, nonviral transfection reagent is needed to deliver viral DNA into cell during viral vector preparation.

Gene transfection reagent is needed to deliver the target gene into a cell during gene transfection. Calcium phosphate shows low transfection efficiency, and is of no effect for a large number of cell lines, so it doesn't meet the most needs in this field. Presently the most popular gene transfection reagent is cationic lipids and cationic polymers. Both of them can overcome the cellular barriers and carry nucleic acid into cell. Cationic lipids show high transfection efficiency in vitro gene delivery. However, they are not suitable for in vivo administration, because they will be rapidly cleared by the plasma, moreover they can accumulate within the lung tissue and induce potent anti-inflammatory activity in vivo, which will induce high level of toxicity. Owing to above limitation of cationic lipid, there is a growing interest in cationic polymer gene carriers.