Bio-nano complexes: DNA/surfactant/single-walled carbon nanotube interactions in electric field

Bio-nano complexes of calf-thymus DNA with a cationic surfactant (DNA/DTAB) and with surfactant wrapped single-walled carbon nanotubes (DNA/SD) were prepared and investigated. The focus of this study was on the molecular interactions, dynamics and binding characteristics as evaluated by a battery of experimental techniques. The major binding sites on DNA and their binding affinities toward the surfactant (DTAB) are identified by Fourier Transform InfraRed (FTIR) spectroscopy. DTAB molecules display higher binding affinity toward DNA when hydrophobically attached to the single-walled carbon nanotube (SWNT) surface. Dielectric spectroscopy of the neat DNA and the two complexes revealed the presence of a process assigned to the motions of counterions distributed along the DNA backbone. The time scale of this process is a function of the composition of the complex and is shortest at a particular DNA/DTAB or DNA/SD ratio. The effect of SWNT on the zeta potential and the hydrodynamic diameter is manifested by the speed-up of charge reversal and a large complex size at the iso-electric point (IEP). The secondary structure of DNA is altered by the presence of SWNTs; however, there is no evidence of the transition of DNA in either complex from type B to other forms.