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Suspension characterization of synthetic nanoparticles under physiological conditions as a tool for toxicological studies

: Meißner, T.; Potthoff, A.; Richter, V.

Bundesministerium für Bildung und Forschung -BMBF-; European Commission:
Nanotechnology in industrial applications. EuroNanoForum 2007 : European and International Forum on Nanotechnology; Proceedings of the forum organized by the Federal Ministry of Education and Research, Germany, with the support of the European Commission, held in Düsseldorf on 19 - 21 June 2007
Luxembourg: Office for Official Publications of the European Communities, 2007 (EUR 22833)
ISBN: 978-92-79-05481-5
Reportnr.: KI-NA-22833-EN-C
European and International Forum on Nanotechnology (EuroNanoForum) <3, 2007, Düsseldorf>
Fraunhofer IKTS ()
Adsorption; agglomeration; bovine serum albumin; nanoparticle; Protein; suspension stability; tungsten carbide; toxicity; toxicologial study; Zetapotential

Due to their outstanding properties nanoscale particles can be found in many applications in medicine, cosmetics, electronics, environmental protection, civil engineering and material science. However, a critical view on possible risks of nanoparticles for the environment and human health is necessary. Our work is focused on the chemical-physical characterization of engineered nanoparticles like ceramics, hard materials such as tungsten carbide (WC) with and without cobalt, metals like platinum as well as carbon nanotubes, and their behaviour in physiological media. The results are used later on to describe and interpret the interaction of the particles with cells. The investigations are a part of the BMBF funded project INOS.
Our focal point with reference of health aspects is to study the behaviour of nanoparticles in physiological solutions. The interest of our research is to describe the interactions of the particles itself and reactions of nanoparticles with blood constituents such as proteins.
The particle size distribution is measured using dynamic light scattering, which allows the detection of nanosized particles. Besides the size, the surface charge of these nanoparticles has a significant function. The particle's surface charge is describable with zeta potential which can be obtained by measuring the electrophoretic particle movement. A specific attribute of physiological solutions is their high electrolyte concentration that causes a reduction of the electrochemical double layer down to 1nm according to the Debye-Hückel theory. Therefore, the particles converge and agglomerate because the double layer repulsive force is smaller than the van-der-Waals attractive force which can be explained by the DLVO theory.
The figure shows the agglomeration activity of tungsten carbide particles in phosphate buffer (PBS). In pure buffer solution agglomerates are formed within a short time as expected from DLVO theory. The agglomeration action is clarified by the low absolute value of the measured zeta potential (-20mV). If the phosphate buffer additionally contains albumin (BSA) in various concentrations, no agglomeration was obtained, although the measured zeta potential waslower than in BSA-free suspension. Interestingly, the zeta potential of BSA in PBS (~ -8mV) is nearly the same compared to the WC-BSA suspension (~ -11mV). Proteins do not agglomerate under physiological salt concentrations because they are not only stabilized electrostatically but also sterically. Obviously, BSA adsorbs on the Figure: Particle size of tungsten carbide
particle's surface, assigns their steric ability to the new formed WC-(cWC = 0.05 mg/ml) in phosphate buffer depending on the presence of BSA
BSA-particle, and stabilizes the suspension in that way. The same results have been achieved in culture medium DMEM containing 10 % FBS, which partly consists of proteins.
As one can see, the behaviour of nanoparticles has to be characterized under appropriate physiological conditions in order to be able to interpret results of toxicological studies.