Development and assessment of nanoparticle suspensions as fundament for toxicological analysis

A comprehensive physical-chemical characterization of nanomaterials is the requirement to assess possible risks of nanomaterials. Therefore, we developed a test strategy which gives toxicologist information on the status of nanoparticles. First of all, the powder itself is characterized which means the determination of particle form, size and aggregation state as well as of the specific surface area and crystallinity. In the second step, we prepare a non-physiological electrostatically stabilized initial nanoparticle suspension. The stability is estimated by zeta potential measurements. Hence, a pH adjustment or an addition of a non-toxic dispersant is done to reach high absolute values of the zeta potential. After that, the suspension is sonicated to destroy agglomerates into smallest dispersable units. The size distribution of these units is measured by means of dynamic light scattering. Now, this stable well-defined initial suspension is added to the appropriate physiological media according to the in vitro or in vivo background. In protein-free media, all tested particles agglomerate. In the presence of BSA or FBS an agglomeration can be slowed or inhibited. When having a sufficient protein amount, the nanoparticles stay stable under these conditions for days. Finally, these findings give a better knowledge of the status of nanoparticles under physiological conditions and allow a standardized procedure in toxicological testing. This enables an improved interpretation of in vitro and in vivo data to explain mechanisms of nanoparticle toxicity. The results are demonstrated at technical ceramic nanoparticles.