Ge S, Kojio K, Takahara A, Kajiyama T
Department of Materials Physics and Chemistry, Graduate School of Engineering, Kyushu University, Fukuoka, Japan.
J Biomater Sci Polym Ed. 1998;9(2):131-50. doi: 10.1163/156856298x00479.
Octadecyltrichlorosilane (OTS) and [2-(perfluorooctyl)ethyl]trichlorosilane (FOETS) monolayers and their mixed monolayer were polymerized on a water subphase and subsequently immobilized onto a silicon wafer surface by covalent bonding. Atomic force microscopic (AFM) observation of the mixed (OTS/FOETS) monolayer revealed the formation of a phase-separated structure. Protein-adsorption behavior onto the monolayers was investigated in situ on the basis of an attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopic flow cell method and the morphology of the monolayer surface-adsorbed bovine serum albumin (BSA) was observed by AFM. Protein adsorption behavior observed by ATR-FT-IR flow cell method revealed that the amount of BSA adsorption onto the OTS and FOETS monolayers increased remarkably at an initial experimental stage and attained a steady state within a few minutes at pH 7.5. The amount of steady state adsorption was c. 0.18-0.2 microgcm(-2). AFM observation of the monolayer after exposure to BSA solution suggested that BSA adsorbed in the end-on adsorption state on OTS monolayer and side-on one in the FOETS monolayer, respectively. However, in the case of the mixed (OTS/FOETS) monolayer, ATR-FT-IR flow cell experiment revealed that the amount of steady state adsorption of BSA was suppressed. Also, AFM observation revealed that at pH 7.5, BSA preferentially adsorbed onto the FOETS phase of the mixed (OTS/FOETS) monolayer, which had a higher interfacial free energy against water. On the other hand, BSA adsorbed homogeneously onto the OTS and FOETS phases at the isoelectric point of BSA (pH 4.7). These results indicate that the preferential adsorption of BSA onto the FOETS phase in the mixed (OTS/FOETS) monolayer system is due to: (1) the minimization of the interfacial free energy between a monolayer surface and an aqueous solution; and (2) the electrostatic repulsion between BSA molecules bearing negative charges.
十八烷基三氯硅烷（OTS）和[2-（全氟辛基）乙基]三氯硅烷（FOETS）单分子层及其混合单分子层在水亚相上进行聚合，随后通过共价键固定在硅片表面。原子力显微镜（AFM）对混合（OTS/FOETS）单分子层的观察揭示了相分离结构的形成。基于衰减全反射傅里叶变换红外（ATR-FT-IR）光谱流动池法，原位研究了蛋白质在单分子层上的吸附行为，并通过AFM观察了单分子层表面吸附牛血清白蛋白（BSA）的形态。通过ATR-FT-IR流动池法观察到的蛋白质吸附行为表明，在初始实验阶段，BSA在OTS和FOETS单分子层上的吸附量显著增加，并在pH 7.5下几分钟内达到稳态。稳态吸附量约为0.18 - 0.2 μg/cm²。暴露于BSA溶液后对单分子层的AFM观察表明，BSA分别以端对端吸附状态吸附在OTS单分子层上，以侧对侧吸附状态吸附在FOETS单分子层上。然而，对于混合（OTS/FOETS）单分子层，ATR-FT-IR流动池实验表明，BSA的稳态吸附量受到抑制。此外，AFM观察表明，在pH 7.5时，BSA优先吸附在混合（OTS/FOETS）单分子层的FOETS相上，该相具有较高的与水的界面自由能。另一方面，在BSA的等电点（pH 4.7）时，BSA均匀地吸附在OTS和FOETS相上。这些结果表明，在混合（OTS/FOETS）单分子层体系中，BSA优先吸附在FOETS相上的原因是：（1）单分子层表面与水溶液之间的界面自由能最小化；（2）带负电荷的BSA分子之间的静电排斥。
