(Intra)Cellular Stability of Inorganic Nanoparticles: Effects on Cytotoxicity, Particle Functionality, and Biomedical Applications

An overview of the current understanding of the behavior of iron oxide nanoparticles (IONPs), Q-Dots, silver and ZnO NPs, and Au NPs as a result of highly varying conditions to which they will be exposed when used in biomedical research or when distributed in the environment. It was shown that depending on the nature of the core material degradation of the NPs can occur, and its extent depends on the microenvironment to which they are exposed. In this connection, distinction should be made between degradation of the inorganic core, which highly depends on the material of the core, and degradation of the organic surface coating, which in particular affects colloidal stability and thus biodistribution of the NPs. For degrading NPs, the process of degradation brings along substantial difficulties in understanding their toxicological profile as not only the NP but also its released ions and the combination of the two can all have different biodistributions and toxic effects, which must be studied in detail. Other focus points are NP shape and size, where the ratio of surface area over volume should be kept as low as possible as degradation will occur at the surface of the NPs. Furthermore, the composition of the chemical core can be adjusted by the addition of other metal ions and hereby altering the matrix of the inorganic cores, which can result in enhanced chemical stability against pH-dependent degradation.