Templating Iron(III) Oxides on DNA Molecules.

Fe(III) oxides were prepared as free nanoparticles and on DNA templates via the precipitation of Fe(III) salts with NaOH in the presence/absence of DNA. Through control of the pH and temperature, FeOOH and FeO were synthesised. The formation of templated materials FeOOH/DNA and FeO/DNA was confirmed using UV-Vis absorption and FTIR spectra. The direct optical gap of FeO/DNA was estimated as 3.2 eV; the absorption by FeOOH/DNA and FeO/DNA at longer wavelengths is weaker, but consistent with indirect gaps near 2 eV. X-ray photoelectron spectra confirmed the presence of Fe(III) and DNA in the templated samples. Analysis of the X-ray diffraction patterns of both templated and non-templated FeOOH and FeO demonstrated that the materials were the -FeOOH and -FeO polymorphs with crystallite diameters of the DNA-templated materials estimated as 7.6 nm and 6.8 nm. Transmission electron microscopy showed needle-like crystals of both FeOOH and FeO, but the FeO contains some globular structures. In contrast, the morphology of FeOOH/DNA and FeO/DNA consists of needle-like crystallites of the respective oxides organised into complex dendritic structures with a length on the 10 μm scale formed by the DNA molecules. Finally, scanned conductance microscopy provided evidence for the conductivity of the FeOOH/DNA after alignment via molecular combing on an Si/SiO substrate. FeO/DNA did not exhibit any detectable conductivity.