School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis, Oregon, United States of America.
Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis, Oregon, United States of America.
PLoS One. 2020 Jun 3;15(6):e0233844. doi: 10.1371/journal.pone.0233844. eCollection 2020.
The hydrophobicity of nanoparticles (NPs) is a key property determining environmental fate, biological partitioning and toxicity. However, methods to characterize surface hydrophobicity are not uniformly applied to NPs and cannot quantify surface changes in complex environments. Existing methods designed to evaluate the hydrophobicity of bulk solids, chemicals, and proteins have significant limitations when applied to NPs. In this study, we modified and evaluated two methods to determine the hydrophobicity of NPs, hydrophobic interaction chromatography (HIC) and dye adsorption, and compared them to the standard octanol-water partitioning protocol for chemicals. Gold, copper oxide, silica, and amine-functionalized silica NPs were used to evaluate methods based on their applicability to NPs that agglomerate and have surface coatings. The octanol water partitioning and HIC methods both measured Au NPs as hydrophilic, but despite having a small size and stable suspension, NPs could not be fully recovered from the HIC column. For the dye adsorption method, hydrophobic (Rose Bengal) and hydrophilic (Nile Blue) dyes were adsorbed to the NP surface, and linear isotherm parameters were used as a metric for hydrophobicity. CuO was determined to be slightly hydrophilic, while SiO2 was hydrophilic and Ami-SiO2 was hydrophobic. The advantages and limitations of each method are discussed, and the dye adsorption method is recommended as the most suitable for application across broad classes of nanomaterials. The dye assay method was further used to measure changes in the surface hydrophobicity of TiO2 NPs after being suspended in natural water collected from the Alsea Rivers watershed in Oregon. TiO2 NPs adsorbed Rose Bengal when suspended in ultrapure water, but adsorbed Nile Blue after being incubated in natural water samples, demonstrating a shift from hydrophobic to hydrophilic properties on the outer surface. The dye adsorption method can be applied to characterize surface hydrophobicity of NPs and quantify environmental transformations, potentially improving environmental fate models.
纳米粒子（NPs）的疏水性是决定其环境归宿、生物分配和毒性的关键特性。然而，用于表征表面疏水性的方法并没有统一应用于 NPs，并且不能量化复杂环境中的表面变化。现有的用于评估块状固体、化学品和蛋白质疏水性的方法在应用于 NPs 时存在显著的局限性。在这项研究中，我们改进并评估了两种用于确定 NPs 疏水性的方法，疏水相互作用色谱（HIC）和染料吸附，并将其与化学品的标准辛醇-水分配协议进行了比较。金、氧化铜、二氧化硅和胺功能化二氧化硅 NPs 被用于评估基于其对聚集和表面涂层的 NPs 的适用性的方法。辛醇-水分配和 HIC 方法均将 Au NPs 测量为亲水性，但尽管 NPs 具有较小的尺寸和稳定的悬浮液，但仍无法从 HIC 柱中完全回收。对于染料吸附方法，疏水性（孟加拉玫瑰红）和亲水性（尼罗蓝）染料被吸附到 NP 表面，线性等温线参数被用作疏水性的度量。CuO 被确定为略微亲水性，而 SiO2 是亲水性的，Ami-SiO2 是疏水性的。讨论了每种方法的优缺点，并推荐染料吸附方法最适合应用于广泛的纳米材料类别。该染料测定法进一步用于测量在俄勒冈州艾尔西河流域采集的天然水中悬浮后 TiO2 NPs 的表面疏水性变化。TiO2 NPs 在超纯水中悬浮时吸附孟加拉玫瑰红，但在天然水样中孵育后吸附尼罗蓝，表明外表面的疏水性到亲水性性质的转变。染料吸附法可用于表征 NPs 的表面疏水性并量化环境转化，从而可能改进环境归宿模型。
