Center for Environmental Nanoscience and Risk, Arnold School of Public Health, University South Carolina, Columbia, SC 29208, United States; Department of Environmental Health Sciences, Arnold School of Public Health, University South Carolina, Columbia, SC 29208, United States.
Department of Epidemiology and Biostatistics, Arnold School of Public Health, University South Carolina, Columbia, SC 29208, United States.
J Colloid Interface Sci. 2017 Feb 1;487:192-200. doi: 10.1016/j.jcis.2016.10.037. Epub 2016 Oct 17.
Nanomaterial (NM) aggregation is a key process determining their environmental, fate behavior and effects. Nanomaterials are typically engineered to remain kinetically stable; however, in environmental and toxicological media, NMs are prone to aggregation. The aggregation kinetics of NM is typically quantified by measuring their attachment efficiency (α) and critical coagulation concentration (CCC). Several studies measured α and CCC for Ag NMs with a major focus on investigating the effects of ionic strength, ion valency and natural organic matter, with few studies investigating other environmental factors such as light and dissolved oxygen and none investigating the effect of particle size, buffer type and concentration, or surface coverage by capping agent. A survey of recent research articles reporting CCC values for Ag NMs reveals substantial variation in experimental conditions and particle stability with CCC values of monovalent and divalent counterions covering a wide range (ca. 25 to infinity for monovalent counterions and 1.6 to infinity for divalent counterions). Here, we rationalize the differences in the CCC values for Ag NMs based on the variability in the experimental conditions, which includes NM and medium physicochemical properties. Capping agents determines NM stability mechanism with citrate, sodium dodecyl sulfate (SDS), and alginate stabilizing NM by electrostatic mechanism; whereas polyvinylpyrrolidone (PVP), casein, dextrin, tween, branched polyethyleneimine (BPEI), and Gum Arabic stabilizing NMs by steric mechanisms. The CCC values for Ag NMs with different capping agents follow the order citrate∼alginate∼SDS<casein<dextrin<PVP<tween<branched polyethyleneimine (BPEI)∼gum Arabic. For charge stabilized Ag NMs, the CCC increases with the decrease in NM size and buffer concentration and decreases with light irradiation. For sterically stabilized PVP-Ag NMs, the CCC increases with the coating concentration/surface coverage and completely coated Ag NMs do not undergo aggregation even at high salt concentrations.
纳米材料（NM）的聚集是决定其环境、命运和效应的关键过程。纳米材料通常被设计为保持动力学稳定；然而，在环境和毒理学介质中，纳米材料容易聚集。纳米材料的聚集动力学通常通过测量其附着效率（α）和临界聚集浓度（CCC）来定量。几项研究测量了 Ag NM 的α和 CCC，主要集中在研究离子强度、离子价和天然有机物的影响上，很少有研究调查其他环境因素，如光和溶解氧，也没有研究调查粒径、缓冲液类型和浓度或覆盖有封端剂的表面覆盖率的影响。最近研究文章中报告的 Ag NM CCC 值的调查显示，实验条件和颗粒稳定性存在很大差异，单价和二价抗衡离子的 CCC 值范围很广（单价抗衡离子约为 25 到无穷大，二价抗衡离子为 1.6 到无穷大）。在这里，我们根据实验条件的可变性，包括 NM 和介质物理化学性质，对 Ag NM 的 CCC 值差异进行了合理化。封端剂决定了 NM 的稳定性机制，柠檬酸盐、十二烷基硫酸钠（SDS）和海藻酸钠通过静电机制稳定 NM；而聚乙烯吡咯烷酮（PVP）、酪蛋白、糊精、吐温、支化聚乙烯亚胺（BPEI）和阿拉伯胶通过空间位阻机制稳定 NM。具有不同封端剂的 Ag NM 的 CCC 值遵循以下顺序：柠檬酸盐∼海藻酸盐∼SDS<酪蛋白<糊精<PVP<吐温
支化聚乙烯亚胺（BPEI）∼阿拉伯胶。对于带电荷稳定的 Ag NM，CCC 值随 NM 尺寸和缓冲液浓度的减小而增大，随光照的减小而减小。对于带空间位阻稳定的 PVP-Ag NM，CCC 值随涂层浓度/表面覆盖率的增加而增加，完全包覆的 Ag NM 即使在高盐浓度下也不会聚集。
