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Physico-chemical characterization in the light of toxicological effects

Toxicological investigations on nanoparticles require a comprehensive physico-chemical characterization to get useful information about the powder as well as the behavior of the suspended nanoparticles in water and physiological media. Therefore, we characterized the often used TiO2 P25 and developed procedures to get stable, homogeneous, and well-defined nanoparticle suspensions. A titration of the zeta potential as a function of the pH yielded the conclusion that the TiO2 suspension is stable at a pH of 4 or lower. In this region the zeta potential is higher than 30 mV, which guarantees a high stability of the suspended particles. Hence, a stable TiO2 initial suspension was prepared in 0.1 mM HCl having a mean particle size of 170 ± 5 nm, which was determined by dynamic light scattering. Furthermore, the initial suspension was added to different physiological media (0.9% NaCl solution, phosphate-buffered saline [PBS], Hanks balanced salt solution [HBSS], Dulbecco’s modified Eagle’s medium [DMEM]) for studying the agglomeration behavior. As a result, the agglomeration kinetics at the same TiO2 concentration is independent of the used media. Investigations with PBS containing bovine serum albumin (BSA) and DMEM supplemented with 10% FBS revealed that these protein additions inhibit the agglomeration of the particles. Thus, the physiological media contains particles that are stabilized through the steric or electrosteric effect of BSA and of the proteins in FBS, respectively. Consequently, the particles keep their size from the initial suspension. Finally, our procedure demonstrated on TiO2 P25 results in homogeneously suspended particles in physiological media. This definite status of the particles means an improvement for toxicological testing and understanding.