Abstract: The interaction between cetyltrimethylammonium bromide(CTAB) and λ-DNA was studied by SEM and AFM. It is clear that λ-DNA molecules exhibit discrete conformational change between the coil and globule states with the addition of cationic surfactant. When the concentration of CTAB is less than 2×10^-6mol/L, all DNAmolecules exhibit the extended coil state. Whereas, when the CTAB concentration is higher than 8.0×10^-6mol/L, only compacted DNA molecules in the globular state are observed. To study of coil globule transition, the process of the structural change from the coilinto the globule state is observed under the spatial gradient of the CTABconcentration. The formation of aggregates from two or more globules is noticed at high concentrations of surfactant above 8.0×10^-5mol/L. The surfactant λ-DNA complex has a hydrophobic region akin to ordinary micelle.

Key words: Cationic surfactant, Scanning electron microscopy, Atomic force microscopy