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For the investigation of the interaction of nanoparticles with biomolecules, cells, organs, and animal models there is a need for well-characterized nanoparticle suspensions. In this paper we report the preparation of monodisperse dense amorphous silica nanoparticles (SNP) suspended in physiological media that are sterile and sufficiently stable against aggregation. SNP sols with various particle sizes (2−335 nm) were prepared via base-catalyzed hydrolysis and polymerization of tetraethyl orthosilicate under sterile conditions using either ammonia (Stöber process(1)) or lysine catalyst (Lys-Sil process(2)). The series was complemented with commercial silica sols (Ludox). Silica nanoparticle suspensions were purified by dialysis and dispersed without using any dispersing agent into cell culture media (Dulbecco’s Modified Eagle’s medium) containing antibiotics. Particle sizes were determined by dynamic light scattering. SNP morphology, surface area, and porosity were characterized using electron microscopy and nitrogen adsorption. The SNP sols in cell culture medium were stable for several days. The catalytic activity of the SNP in the conversion of hydrogen peroxide into hydroxyl radicals was investigated using electron paramagnetic resonance. The catalytic activity per square meter of exposed silica surface area was found to be independent of particle size and preparation method. Using this unique series of nanoparticle suspensions, the relationship between cytotoxicity and particle size was investigated using human endothelial and mouse monocyte−macrophage cells. The cytotoxicity of the SNP was strongly dependent on particle size and cell type. This unique methodology and the collection of well-characterized SNP will be useful for further in vitrostudies exploring the physicochemical determinants of nanoparticle toxicity. [ABSTRACT FROM AUTHOR]

Concentrated clear solutions, as used for the preparation of Silicalite-1 zeolite, were synthesized from tetrapropylammonium hydroxide, tetraethylorthosilicate, and water. The solutions were analyzed using three techniques:  quantitative 29Si NMR, synchrotron small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS). 29Si NMR showed the coexistence of silicate oligomers and particles. For the first time, both fractions were analyzed simultaneously, providing a global, quantitative description of the clear solution microstructure. The SAXS patterns, typical of interacting particles, could be used together with the 29Si NMR deduced particle volume fraction to estimate a particle size. A careful analysis of DLS data of the dynamics of the suspensions revealed the occurrence of two diffusive processes. The faster process is a collective particle diffusion. The slower process corresponds to the particle self-diffusion and is present because of the presence of polydispersity in size, shape, and/or surface charge. The self-diffusion coefficient provides a means to estimate the equivalent hydrodynamic radius. The observations hence reveal a complex, polydisperse mixture of particles present at the onset of the Silicalite-1 zeolite formation. Implications on the proposed zeolite formation mechanisms are briefly discussed. [ABSTRACT FROM AUTHOR]