Physicochemical and biological characterization of single-walled and double-walled carbon nanotubes in biological media.

To study the toxicity of nanoparticles under relevant conditions, it is important to reproducibly disperse nanoparticles in biological media in in vitro and in vivo studies. Here, single-walled nanotubes (SWNTs) and double-walled nanotubes (DWNTs) were physicochemically and biologically characterized when dispersed in phosphate-buffered saline (PBS) and bovine serum albumin (BSA). BSA-SWNT/DWNT interaction resulted in a reduction of aggregation and an increase in particle stabilization. Based on the protein sequence coverage and protein binding results, DWNTs exhibited higher protein binding than SWNTs. SWNT and DWNT suspensions in the presence of BSA increased interleukin-6 (IL-6) levels and reduced tumor necrosis factor-alpha (TNF-α) levels in A549 cells as compared to corresponding samples in the absence of BSA. We next determined the effects of SWNTs and DWNTs on pulmonary protein modification using bronchoalveolar lavage fluid (BALF) as a surrogate collected form BALB/c mice. The BALF proteins bound to SWNTs (13 proteins) and DWNTs (11 proteins), suggesting that these proteins were associated with blood coagulation pathways. Lastly, we demonstrated the importance of physicochemical and biological alterations of SWNTs and DWNTs when dispersed in biological media, since protein binding may result in the misinterpretation of in vitro results and the activation of protein-regulated biological responses.

Influence of thermal treatment on nanostructured gold model catalysts.

We fabricated films of Au onto single crystal alumina (Al(2)O(3)(0001)) and nanostructured the surface using a high resolution focused ion beam (FIB) to remove specific regions of the film. The nanostructures consist of lines and orthogonal lines cut into the film, resulting in one- and two-dimensional islands of gold. When these films are heated above 300 °C, small nanoparticles of gold form due to the dewetting of the Au film from the alumina surface. The dimensions of these islands are dictated by the nature of the nanopatterning. The isolated islands generally have the smallest nanoparticles after heating, while the unpatterned film has much larger particles. Sintering is reduced within the nanostructured metal domains due to isolation of Au islands from each other. The evaporation rate is higher within these islands, due to the smaller size of nanoparticles and hence the higher effective vapor pressure over the surface (the Kelvin effect).

Effects of the nanostructuring of gold films upon their thermal stability.

We report results relating to the thermal stability of nanoparticles and show a remarkable effect of nanostructuring of the metal. Au films are nanostructured by focused ion beam sputtering (FIB) to produce isolated areas of metal, which are imaged by atomic force microscopy (AFM). Images of the surface show that, if the islands are made small enough, the metal in the islands is lost by evaporation, whereas the nonfabricated areas outside are relatively stable and the nanoparticles remain present there.