Preparation and Electron Conductivity of DNA-Aligned Cast and LB Films from DNA-Lipid Complexes

Abstract

We describe here a simple preparation of a DNA-lipid complex that is soluble in organic media, and preparations of DNA-aligned thin films from the cast-stretching method and the Langmuir--Blodgett (LB) method. The DNA-lipid complex in which counter cations of phosphate anions are changed to cationic lipophilic amphiphiles was prepared by simply mixing aqueous solutions of DNA and cationic amphiphiles. The DNA-lipid complex is soluble and forms a double-strand structure in organic solutions. A self-standing, water-insoluble DNA-lipid film could be prepared by casting from the organic solution or a hot-press method, and DNA strands were easily aligned in the film by stretching it in one direction. Another method of preparing DNA-aligned thin film is the LB method: anionic DNA strands are transferred with cationic lipid monolayers at the air-water interface by the vertical dipping method and DNA strands are aligned along the dipping direction. The film structure was confirmed by X-ray diffraction, CD spectra of DNA strands, and polarized absorption spectra of intercalated dye molecules. The aligned-DNA film showed a large anisotropic and ohmic electric current (10⁻³ S cm⁻¹, A⊥/A// = 10⁵) along stacked base-pairs of DNA strands aligned in the film. The large anisotropic photo current could also be observed through DNA strands with acridine orange intercalators depending on visible photo irradiation.