Because of its high surface activation energy, nanomaterials tend to have a tendency to reunite. The degree of reunion can be reduced by surface modification. The agglomeration behavior of Zinc Oxide nanoparticles has a crucial impact on its toxicity, because agglomeration determines the effective concentration and size of Zinc Oxide nanoparticles. So far, there has been no systematic study of the aggregation behavior of Zinc Oxide nanoparticles in the biological environment. However, in a number of studies, the size of Zinc Oxide nanoparticles in the solution phase has been reported. The degree of aggregation and aggregation kinetics of Zinc Oxide nanoparticles in the solution can be monitored by laser dynamic light scattering (DLS) and other techniques. The published results show that the Zinc Oxide nanoparticles have serious reunion in the solution phase.
According to the editor's study, Zinc Oxide nanoparticles can only be suspended in water for a few minutes in a more stable way. The suspension time and dispersion uniformity of the Zinc Oxide nanoparticles are better than the micron Zinc Oxide, which is similar to that of other nanomaterials. It also suggests that the exposure concentration of Zinc Oxide nanoparticles in actual exposure is likely to be higher than the micron Zinc Oxide. Although Den9 and other reports have reported that Zinc Oxide will adsorb protein, the addition of protein does not significantly improve the aggregation of Zinc Oxide nanoparticles. In the DMEM medium containing serum, the particle size of Zinc Oxide nanoparticles can only be reduced from about 600 nm in PBS to about 300 nm. In the study, the editor found that Zinc Oxide nanoparticles still had Yan Zhongju precipitation in a medium containing 10% calf serum. In Zhu and other studies, they also found that Zinc Oxide nanoparticles gathered. These aggregated Zinc Oxide almost reached sedimentation equilibrium after 3 h, and more than 80% of Zinc Oxide appeared in sediments.
The results of measuring the particle size of Zinc Oxide nanoparticles by DLS also show that the agglomeration of Zinc Oxide nanoparticles is serious, that is, the result of the hydration radius is greater than that of the TEM. But it is important to note that DLS does not necessarily reflect the size of Zinc Oxide nanoparticles, so DLS results need to be treated carefully. For example, Lin et al. [3] found that in the Ham SF-12 medium, Zinc Oxide nanoparticles (diameter 70 nm) and micron Zinc Oxide (diameter 420 nm) were similar in size, and the particle size at 10 / 19 / mL was about 100 nm, which was smaller than the diameter of micron Zinc Oxide itself. This result is obviously unreasonable and needs more research to explain this contradiction. Their study also showed that the Zinc Oxide nanoparticles were easy to settle, especially at the concentration of 100 Ft9 / mL. The particle sizes of the two parallel tests are 900 nm and 300 nm respectively, indicating that the system is very unstable, and it is still easy to sink under the ultrasonic condition.
In the dry air, the Zinc Oxide nanoparticles are easily dispersed, forming a form similar to the ultrafine Zinc Oxide dust, which is easily inhaled. In this respect, Zinc Oxide nanoparticles are more likely to form dust than micron Zinc Oxide, dispersed in the air, and then cause lung toxicity. The related research, especially the research on the formation of dust from Zinc Oxide nanoparticles, is very small. The current comparative study of Zinc Oxide nanoparticle and micron Zinc Oxide respiratory toxicity is mainly through the way of tracheal drip, ignoring the factors that make Zinc Oxide nanoparticles easier to form dust in the air. Considering the size of Zinc Oxide nanoparticles, we speculate that Zinc Oxide nanoparticles may have higher effective exposure concentration, which will cause greater respiratory toxicity.