A study of Na-DNA films containing NaCl via scanning electron and tunneling microscopies

Unoriented films of Na-DNA were prepared by dessicating a gel with different amounts of NaCl. For low salt concentrations, the resulting films were smooth and patternless. For high salt concentrations, the resulting films had visible patterns that were very similar to those recently reported by Sclavi et al. [(1994) Biopolymers, Vol. 34, pp. 1105-1113]. Scanning electron and tunneling microscopies and electron dispersive spectroscopy studies were used to study the spatial distribution of NaCl throughout these films. Two main conclusions were reached about the NaCl: (1) some NaCl is distributed throughout every film, and (2) the visible patterns observed in films with a large amount of NaCl were caused by the growth of NaCl crystals during the dehydration process.