The control of the DNA condensation process is essential for compaction of DNA in chromatin, as well as for biological applications such as nonviral gene therapy. This review endeavours to reflect the progress of investigations on DNA condensation effects of nanostructure-based condensing agents (such as nanoparticles, nanotubes, cationic polymer and peptide agents) observed by using atomic force microscopy (AFM) and other techniques. The environmental effects on structural characteristics of nanostructure-induced DNA condensates are also discussed.

Nonviral vectors are highly desirable for the development of efficient gene delivery systems. In this study, we report the monomolecular condensation of plasmid DNA and efficient cell transfection by imidazolium gemini surfactants ([C12-4-C12im]Br2), which could be a potential nonviral vector for efficient gene therapy. Homogeneous DNA/[C12-4-C12im]Br2 nanoparticles are formed with a diameter of approximately 100 nm and investigated by using atomic force microscopy. DNA condensates evolve from supercoiled DNA molecules, to individual toroids, to close-packed particles, and eventually to multimolecular aggregates with the increase of [C12-4-C12im]Br2 concentrations. Highly efficient gene transfection in vitro is demonstrated in human embryonic kidney 293 (HEK293) and HeLa cells, which could be attributed to the effective DNA condensation into uniform nanoparticles induced by [C12-4-C12im]Br2. In addition, the low cytotoxicity of [C12-4-C12im]Br2 at transfection concentration region verified by cell viability assay (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide, MTT assay) also supports [C12-4-C12im]Br2 as an effective gene vector. The high gene transfection efficiency by [C12-4-C12im]Br2 as well as its low cytotoxicity could shed light on the rational molecular design of nonviral vectors for gene delivery systems.