Morphology characterization and single-molecule study of DNA-dodecyltrimethylammonium bromide complex.

DNA compaction induced by dodecyltrimethylammonium bromide (DTAB) is studied using atomic force microscopy (AFM) and magnetic tweezers. The morphology of DNA-DTAB complex is dependent on the DTAB concentration and incubation time. With magnesium ions, the complexes show rod- and network-like structures after approximately 5 min of incubation at low DTAB concentrations. With increasing incubation time, more toroids and globules appeared, resulting in the formation of scattered condensed particles. At high DTAB concentrations, the complexes show swollen globular structures independent of the incubation time. The compaction and unraveling of the DNA-DTAB complex are also analyzed at the single-molecule level using magnetic tweezers. The extension-time curves show a staircase structure with typical sizes of ∼40, 60, 80, and 112 nm, suggesting that the complexes are well organized and more compacted than those induced by multivalent ions. Finally, the high DTAB concentration stabilized the complex and increased the unraveling energy barrier.