Nanocrystalline titanium dioxide (nano-TiO(2)) is an important material used in commerce today. When designed appropriately it can generate reactive species (RS) quite efficiently, particularly under ultraviolet (UV) illumination; this feature is exploited in applications ranging from self-cleaning glass to low-cost solar cells. In this study, we characterize the toxicity of this important class of nanomaterials under ambient (e.g., no significant light illumination) conditions in cell culture. Only at relatively high concentrations (100 microg/ml) of nanoscale titania did we observe cytotoxicity and inflammation; these cellular responses exhibited classic dose-response behavior, and the effects increased with time of exposure. The extent to which nanoscale titania affected cellular behavior was not dependent on sample surface area in this study; smaller nanoparticlulate materials had effects comparable to larger nanoparticle materials. What did correlate strongly to cytotoxicity, however, was the phase composition of the nanoscale titania. Anatase TiO(2), for example, was 100 times more toxic than an equivalent sample of rutile TiO(2). The most cytotoxic nanoparticle samples were also the most effective at generating reactive oxygen species; ex vivo RS species generation under UV illumination correlated well with the observed biological response. These data suggest that nano-TiO(2) samples optimized for RS production in photocatalysis are also more likely to generate damaging RS species in cell culture. The result highlights the important role that ex vivo measures of RS production can play in developing screens for cytotoxicity.

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Interactions between metals and biomacromolecules including proteins, polysaccharides, and nucleic acids are important since they can be essential for a number of natural and industrial phenomena. These range from interactions of highly specific metal cofactors with particular proteins [1] to biosorption of heavy metals by polysaccharide hydrogels.[2]The unique features of DNA have been exploited in the development of novel materials, especially in the areas of medicine and nanotechnology. Classical research concerning antitumor drugs has focussed on the interactions of platinumor ruthenium-containing compounds with the major or minor grooves of polynucleotides. [3][4][5][6] There is a tremendous interest in the use of DNA in nanotechnology as a positioning template for the immobilization of metal nanoclusters with view to future applications in the construction of nanoelectronic devices. [7][8][9][10][11] Herein we report the interaction of Au 55 nanoclusters with the major grooves of B-DNA. The Au 55 clusters are degraded to Au 13 clusters by the transition of B-DNA into A-DNA in ultrahigh vacuum, and the resulting shrinkage of the major grooves. We have performed molecular-dynamics simulations and provided further information on the mechanism by which wires of Au 13 clusters form, and attempt to explain the interwire separation of 0.5 nm.

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Analytical ultracentrifugation (AU) provides a general way to probe the polydispersity of nanoparticles and the formation of bioconjugates in solution. Unconjugated gold nanocrystals show sedimentation coefficient distributions that are in agreement with size distributions as measured by TEM. AU is sensitive to the size/shape changes elicited by conjugation, in this case to lactose repressor (LacI). AU data reveal saturating protein concentrations for conjugates that correspond to the measured stoichiometry of the complex under these conditions.

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