Interactions of titanium dioxide nanotubes (TiO2NTs) with positively (AuNP+s) and negatively charged (AuNP−s) gold nanoparticles have been investigated using a combination of UV-Vis spectroscopy, ζ potential and transmission electron microscopy analyses. Possessing a negatively charged surface, TiO2NTs show no attractive interactions with AuNP−s, but readily form nanostructured composites with AuNP+s. Using different ratios of TiO2NT : AuNP+, the overall charge of nanotube–nanoparticle composite can be tuned from positive through neutral to negative, which drastically affects the solubility of the resultant material in water. The charge of the nano-composite is related to the density of AuNP+s adsorbed on the surface of the TiO2NTs. At higher densities adsorbed nanoparticles interact with each other and exhibit a red-shift of their surface plasmon resonance, the magnitude of which increases with the density of AuNP+s. This methodology enables precise control over the composition, charge and structure of nanotube–nanoparticle materials.
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