Comparative AFM Studies on the Morphology of Conducting Polymers/DNA Templated Nanowires

Abstract

Comparative morphological studies of three conductive polymers (polyimidazole (Plm), polyindole (Pln), and polypyrrole (Ppy)) templated with deoxyribonucleic (DNA) were carried out on silicon (Si)/mica substrate with the aim of finding more insight about the extent of mixing of the polymers with the DNA and the size of the nanowires formed. Atomic force microscope (AFM) height images of bare DNA on pre-treated substrates revealed a two-dimensional network structure with an average height of approximately 1.60 ± 0.01 nm; which is close to the double stranded DNA chain height. Plm/DNA exhibits globular and agglomerate nanostructures for the concentrated polymers, while the diluted form reveals a dispersed network with a diameter of 3 - 5 nm mostly. In Pln/DNA, the AFM images show dense networks of nanowires in their concentrated form, while the diluted samples displayed individual single wires with regular and smooth morphologies. Statistical analysis of the nanowires AFM heights revealed the dominance of wires with diameters in the range of 3 - 4 nm. The most common nanowire height range was 9 - 10 nm. Comparing the three polymer AFM studies, it can be said that polypyrrole has the highest nanowires range of 9 - 10 nm, then Plm/DNA (3 - 5 nm) and the least is Pln/DNA with 3 - 4 nm range. From the nanowire sizes and morphologies (uniform, smooth and continuous), it can be concluded that both polymers have good potentials for DNA templating and application in nanoelectronic devices as they can be aligned on nanoelectrodes for passage of electricity.