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Porous silicon (PSi) particles have been studied for the effects they elicit in Caco-2 and RAW 264.7 macrophage cells in terms of toxicity, oxidative stress, and inflammatory response. The most suitable particles were then functionalized with a novel 18 F label to assess their biodistribution after enteral and parenteral administration in a rat model. The results show that thermally hydrocarbonized porous silicon (THCPSi) nanoparticles did not induce any significant toxicity, oxidative stress, or inflammatory response in Caco-2 and RAW 264.7 macrophage cells. Fluorescently labeled nanoparticles were associated with the cells surface but were not extensively internalized. Biodistribution studies in rats using novel 18 F-labeled THCPSi nanoparticles demonstrated that the particles passed intact through the gastrointestinal tract after oral administration and were also not absorbed from a subcutaneous deposit. After intravenous administration, the particles were found mainly in the liver and spleen, indicating rapid removal from the circulation. Overall, these silicon-based nanosystems exhibit excellent in vivo stability, low cytotoxicity, and nonimmunogenic profiles, ideal for oral drug delivery purposes.

The highly defined morphology of self-organized anodic TiO 2 nanotube layers found in recent years has applications in fields such as biotechnology, [1,2] photo-catalysis, [3,4] or dyesensitized solar cells. [5] While the semiconducting nature of TiO 2 is crucial for many of these applications, the limited conductivity prevents an even broader and efficient use in applications that require a fast electron transport, such as functional electrodes or as electrocatalyst supports. Herein we demonstrate how to overcome this limitation by using a robust carbo-thermal reduction treatment converting the TiO 2 into an oxy carbide compound that shows stable semimetallic conductivity. These TiO x C y nanotubes can be used, for example, as an inert electrode with substantial overpotential for O 2 evolution, or as a highly efficient support for electrocatalytic reactions, such as in methanol-based fuel cells.To produce TiO 2 nanotube layers we use self-organizing electrochemical anodization, [6][7][8][9] a process leading to oxide nanotubes on a range of refractory metals (e.g. titanium, [10] zirconium, hafnium [11,12] ). TiO 2 in its anatase or rutile form is a wide band-gap semiconductor material (E g % 3.0-3.2 eV) and as such particularly suitable for applications based on UV-or X-ray-induced interactions.[13] To achieve enhanced control over the electronic and optical properties of these semiconducting nanotubes, various doping approaches with suitable elements, for example, C [14,15] and N, [16][17][18] or various transition metals [19] were reported. However, for highthroughput electrodes, or electrocatalyst supports, the conventional doping approaches do not provide sufficient electrical conductivity. Herein we use a high-temperature treatment in acetylene that converts the semiconducting anatase phase into carbon rich (MagnØli-type) phases that show semimetallic conductivity. The process can be carried out without loss of the ordered nanotubular morphology as illustrated in Figure 1. In this case self-organized TiO 2 nanotubes were grown with a diameter of 80 nm to a layer Figure 1. SEM images of the nanotubes after a) anodization formation and b) after a thermal acetylene treatment at 850 8C for 10 min. The lower insets are the corresponding cross-sectional views. c) X-ray diffraction results for the acethylene-treated tubes and those of anatase TiO 2 nanotubes and highly C-doped TiO 2 nanotubes. d) XPS spectra showing the Ti 2p peak of thermal-carbonized nanotubes and of anatase TiO 2 nanotubes and highly C-doped TiO 2 nanotubes.

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