Layer-by-layer assembly of nanoblended thin films: Poly(allylamine hydrochloride) and a binary mixture of a synthetic and natural polyelectrolyte

Nanoblended multilayer thin films were formed by the layer-by-layer assembly of poly(allylamine hydrochloride) (PAH) and a binary mixture of single-stranded deoxyribonucleic acid (DNA) and poly(sodium styrenesulfonate) (PSS). UV-vis spectrophotometry was used as a facile means to determine the proportion of DNA and PSS in the films. Films assembled from solutions containing sodium chloride (NaCl) were found to contain predominantly PSS, while the presence of ethanol in the adsorption solution favored the incorporation of DNA into the film. The thickness of the films was determined by using surface plasmon resonance, which revealed increasing film thickness with a larger proportion of DNA in the film. This result was confirmed with quartz crystal microbalance studies, which showed a larger frequency increment for increasing DNA percentage in the film. The suppression of DNA adsorption under conditions of high ionic strength (high NaCl concentration) was shown to be a result of DNA displacement by PSS, which is favored when NaCl is present in the adsorption solution. Atomic force microscopy was used to examine the surface morphology, with films assembled without added salt having rougher surfaces than those prepared from solutions containing NaCl. Increasing the molecular weight of the PSS was shown to increase the proportion of DNA in the film, possibly due to increased chain entanglement between the two species. The reported results are significant in that they demonstrate that film composition can be tuned by adjusting the blend solution composition, adsorption conditions, and polyanion molecular weight to favor the adsorption of a particular species.