A dielectric study of interpolymer complexes of polyaniline and DNA

When positively charged conjugated polymer chains are jointly dispersed with (single-stranded or double stranded) DNA chains in solvents of low polarity, complex hybrid structures can result. Interpolymer complexes (IC) can be formed due to the mutual Coulomb interactions between the positive charges in the doped conjugated polymer and the negatively charged phosphate groups along the external ridge of the nucleotide chains. In fact, some of these IC have been reported as potential candidates for several biotechnological applications as, for instance, the development of reliable methods for determining the precise concentration of DNA, a still acute necessity for a number of applications. In this work, we measure the dielectric response of polyaniline/DNA complexes as a convenient procedure to investigate the dominating mechanisms involved in their process of aggregation when dispersed in chloroform. As the ratio of concentrations [PANI]/[DNA] is progressively increased, the corresponding charge transfer resistance varies in a characteristic way, according to the nature of the microscopic reactions taking place in the solution. In fact, the patterns of variation of the charge transfer resistance and optical absorbance of the solution corresponding to the polaron band transition are quite similar, but exhibiting opposite trends. We take this as strong evidence that the electrical characterization of such IC systems represents an alternative method to conventional spectroscopic techniques for investigating the dominant interaction mechanisms DNA and PANI chains in solutions.