Department of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan.
J Colloid Interface Sci. 2012 Sep 15;382(1):97-104. doi: 10.1016/j.jcis.2012.06.002. Epub 2012 Jun 15.
Gold is known to have good biocompatibility because of its inert activity and the surface property can be easily tailored with self-assembled monolayers (SAMs). In previous works, gold surfaces were tailored with homogeneously mixed amine and carboxylic acid functional groups to generate surfaces with a series of isoelectronic points (IEPs). In other words, by tailoring the chemical composition in binary SAMs, different surface potentials can be obtained under controlled pH environments. To understand how the surface potentials affect the interaction at the interface, a binary-SAMs-modified Au electrode on a quartz crystal microbalance with dissipation detection (QCM-D) was used owing to the high weight sensitivity of QCM-D. In QCM-D, the frequency shift and the energy dissipation are monitored simultaneously to determine the adsorption behaviors of the plasmid DNA to surfaces of various potentials in Tris-buffered NaCl solutions of different pH. The results revealed that the plasmid DNA can be adsorbed on the SAM-modified surfaces electrostatically; thus, in general, the amount of adsorbed plasmid DNA decreased with increasing environmental pH and the decreasing ratio of the amine functional groups on the surfaces owing to weaker positive potentials on the surface. For the high amine-containing surfaces, due to the strong electrostatic attraction, denser films were observed, and thus, the apparent thickness decreased slightly. The negatively charged carboxylic acid surfaces can still adsorb the negatively charged plasmid DNA at some conditions. In other words, the electrostatic model cannot explain the adsorption behavior completely, and the induced dipole (Debye) interaction between the charged and polarizable molecules needs to be considered as well.
金具有良好的生物相容性，这是由于其惰性活性，并且可以通过自组装单分子层（SAMs）轻松地调整其表面性质。在以前的工作中，通过均匀混合胺和羧酸官能团来调整金表面，以生成具有一系列等电点（IEP）的表面。换句话说，通过调整二元 SAMs 中的化学组成，可以在受控 pH 环境下获得不同的表面电势。为了了解表面电势如何影响界面处的相互作用，使用带有耗散检测的石英晶体微天平（QCM-D）上的二元-SAMs 修饰 Au 电极，因为 QCM-D 具有很高的重量灵敏度。在 QCM-D 中，同时监测频率偏移和能量耗散，以确定在不同 pH 的 Tris 缓冲 NaCl 溶液中，各种电势的表面对质粒 DNA 的吸附行为。结果表明，质粒 DNA 可以通过静电吸附在 SAM 修饰的表面上；因此，通常情况下，随着环境 pH 值的增加和表面上胺官能团比例的降低，吸附的质粒 DNA 量减少，这是由于表面上的正电势较弱。对于高含胺表面，由于强静电吸引，观察到更密集的膜，因此，表观厚度略有下降。带负电荷的羧酸表面在某些条件下仍可以吸附带负电荷的质粒 DNA。换句话说，静电模型不能完全解释吸附行为，还需要考虑带电和极化分子之间的诱导偶极（德拜）相互作用。
