National Physical Laboratory, Teddington, Middlesex, UK.
Anal Chem. 2011 Nov 15;83(22):8659-66. doi: 10.1021/ac202110x. Epub 2011 Oct 27.
Protein adsorption at solid surfaces is central to many phenomena of medical and technological interest. The determination of the amount of protein attached to the surface is a critical measurement performed by using a wide range of methods. X-ray photoelectron spectroscopy (XPS) is able to provide a straightforward quantitative analysis of the amount of protein adsorbed as an overlayer on a material surface. While XPS is commonly employed to assess qualitatively the amount of adsorbed protein, this is usually expressed in terms of the elemental fraction (or at. %) of nitrogen calculated using an assumption of depth homogeneity despite the fact that this does not linearly scale with the amount of protein. In this paper, we have shown that thicknesses derived from XPS data linearly correlated with spectroscopic ellipsometry data on the same samples with a scatter of 10%. A straightforward equation to convert the concentration of nitrogen from XPS into an equivalent thickness of a protein film is presented. We highlight some discrepancies in the absolute thicknesses determined by XPS and ellipsometry on dried films and quartz crystal microbalance on wet films, which appear likely to result from the inclusion of a contribution from water in the latter two techniques.
蛋白质在固体表面的吸附对于许多医学和技术相关的现象都非常重要。通过使用各种方法，确定吸附在表面上的蛋白质的量是一项关键的测量。X 射线光电子能谱（XPS）能够提供吸附在材料表面上的蛋白质覆盖层的直接定量分析。虽然 XPS 通常用于定性评估吸附的蛋白质的量，但这通常是根据假设的深度均匀性计算的氮元素分数（或 at. %）来表示的，尽管这与蛋白质的量不成线性比例。在本文中，我们已经表明，从 XPS 数据得出的厚度与相同样品的光谱椭圆测量数据呈线性相关，其分散度为 10%。提出了一个将 XPS 中的氮浓度转换为蛋白质膜等效厚度的简单方程。我们强调了在干燥膜上通过 XPS 和椭圆测量法以及在湿膜上通过石英晶体微天平法确定的绝对厚度之间存在一些差异，这些差异似乎是由于后两种技术中包含了水的贡献所致。
