Extracellular polymeric substances (EPSs) can conform and orient on the surface according to the applied aquatic conditions. While pH elevation usually removes EPSs from membranes, small changes in pH can change the adsorbed EPS conformation and orientation, resulting in a decrease in membrane permeability. Accordingly, EPS layers were tested with localized surface plasmon resonance (LSPR) sensing and quartz crystal microbalance with dissipation monitoring (QCM-D) using a hybrid sensor. A novel membrane-mimetic hybrid QCM-D–LSPR sensor was designed to indicate both “dry” mass and mechanical load (“wet” mass) of the adsorbed EPS. The effect of pH on the EPS layer’s viscoelastic properties and hydrated thickness analyzed by QCM-D corroborates with the shift in EPS areal concentration, Γ_S, and the associated EPS conformation, analyzed by LSPR. As pH elevates, the processes of (i) elevation in EPS layer’s thickness (QCM-D) and (ii) decrease in the EPS areal density, Γ_S (LSPR), provide a clear indication for changes in EPS conformation, which decrease the effective ultrafiltration (UF) membrane pore diameter. This decrease in the pore diameter together with the increase in surface hydrophobicity elevates UF membrane hydraulic resistance.

中文翻译：

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揭示细胞外聚合物对超滤膜污染的 pH 影响：用局部表面等离子共振分析吸附和构象

细胞外聚合物 (EPS) 可以根据应用的水生条件在表面上顺应和定向。虽然 pH 升高通常会从膜中去除 EPS，但 pH 值的微小变化会改变吸附的 EPS 构象和方向，导致膜通透性降低。因此，EPS 层通过使用混合传感器的局部表面等离子共振 (LSPR) 传感和带耗散监测的石英晶体微量天平 (QCM-D) 进行了测试。一种新型的膜模拟混合 QCM-D-LSPR 传感器旨在指示吸附 EPS 的“干”质量和机械负载（“湿”质量）。通过 QCM-D 分析的 pH 值对 EPS 层的粘弹性和水合厚度的影响证实了 EPS 面积浓度 Γ _S的变化，以及相关的 EPS 构象，由 LSPR 分析。随着 pH 值的升高，(i) EPS 层厚度 (QCM-D) 升高和 (ii) EPS 面密度 Γ _S (LSPR) 降低的过程为 EPS 构象的变化提供了明确的指示，这会降低有效超滤（UF）膜孔径。孔径的减小与表面疏水性的增加一起提高了超滤膜的抗水力。