Helmholtz Zentrum München, Institute of Radiation Protection, 85758 Neuherberg, Germany.
ACS Nano. 2011 May 24;5(5):3766-78. doi: 10.1021/nn200112u. Epub 2011 Apr 1.
With very few exceptions, previous nanotoxicity studies implicitly involved the assumption that the techniques developed for risk assessment of hazardous chemical substances can be applied in unchanged form to explore cell response in NP laden media. This misleading approach has the consequence that the actual dose of exposure is ill defined or, more often, completely unknown. Here the effect of gravitational settling on the dose of exposure was explored for commercially available engineered nanostructured matter (nanopowder). Micrometer sized aggregates abundantly present in all nanopowders were fractured as much as possible by probe-type sonication in water or cell culture media. The morphology of cracked aggregates was studied by scanning electron microscopy. Size distributions were determined by dynamic light scattering (DLS). Possible pitfalls encountered in using DLS were documented. Absorbance measurements and optical microscopy served to monitor the rate of gravitational settling on time sales ranging from minutes up to several days. The sonicated particles settled rapidly in all liquid media. At the well bottom, they exhibited intense lateral (two-dimensional) Brownian-like motion, which allowed them to travel large distances. Taken together, the probability for particle-cell contact may be enhanced by a factor of more than 1000 compared to the commonly advocated picture. The very high levels of exposure can give rise to overload effects which are often misinterpreted as evidence of cytotoxicity. To identify the true toxic potential of NPs, future studies must account for these phenomena. It is also argued that stable dispersions of NPs are not required in nanotoxicity studies.
除了极少数例外，以前的纳米毒性研究都隐含着这样一种假设，即用于危险化学物质风险评估的技术可以未经改变地应用于探索纳米颗粒负载介质中的细胞反应。这种误导性的方法导致实际的暴露剂量定义不明确，或者更常见的是完全未知。在这里，研究了重力沉降对商业上可获得的工程纳米结构物质（纳米粉末）暴露剂量的影响。通过探针式超声处理，尽可能地将所有纳米粉末中大量存在的微米大小的团聚体在水中或细胞培养基中破碎。通过扫描电子显微镜研究了破裂团聚体的形态。通过动态光散射（DLS）确定了粒径分布。记录了在使用 DLS 时可能遇到的陷阱。吸光度测量和光学显微镜用于监测在几分钟到几天的时间范围内的重力沉降速率。在所有液体介质中，超声处理后的颗粒迅速沉降。在瓶底，它们表现出强烈的横向（二维）布朗运动，使它们能够移动很远的距离。总的来说，与通常提倡的观点相比，颗粒与细胞接触的可能性可能增加了 1000 多倍。如此高的暴露水平可能会导致过载效应，这些效应常常被误解为细胞毒性的证据。为了确定 NPs 的真正毒性潜力，未来的研究必须考虑到这些现象。还认为，在纳米毒性研究中不需要稳定的纳米颗粒分散体。
