Department of Geoscience, 1215 West Dayton Street, University of Wisconsin, Madison, WI 53706, USA.
J Colloid Interface Sci. 2012 Mar 15;370(1):192-200. doi: 10.1016/j.jcis.2011.12.031. Epub 2011 Dec 17.
Oxide-supported phospholipid bilayers (SPBs) used as biomimetic membranes are significant for a broad range of applications including improvement of biomedical devices and biosensors, and in understanding biomineralization processes and the possible role of mineral surfaces in the evolution of pre-biotic membranes. Continuous-coverage and/or stacked SPBs retain properties (e.g., fluidity) more similar to native biological membranes, which is desirable for most applications. Using neutron reflectivity, we examined the role of oxide surface charge (by varying pH and ionic strength) and of divalent Ca(2+) in controlling surface coverage and potential stacking of dipalmitoylphosphatidylcholine (DPPC) bilayers on the (11 ̅20) face of sapphire (α-Al(2)O(3)). Nearly full bilayers were formed at low to neutral pH, when the sapphire surface is positively charged, and at low ionic strength (I=15 mM NaCl). Coverage decreased at higher pH, close to the isoelectric point of sapphire, and also at high I≥210 mM, or with addition of 2mM Ca(2+). The latter two effects are not additive, suggesting that Ca(2+) mitigates the effect of higher I. These trends agree with previous results for phospholipid adsorption on α-Al(2)O(3) particles determined by adsorption isotherms and on single-crystal (10 ̅10) sapphire by atomic force microscopy, suggesting consistency of oxide surface chemistry-dependent effects across experimental techniques.
氧化层支撑的磷脂双层（SPB）作为仿生膜在广泛的应用中具有重要意义，包括改善生物医学设备和生物传感器，以及理解生物矿化过程和矿物表面在原始生物膜进化中的可能作用。连续覆盖和/或堆叠的 SPB 保留了更类似于天然生物膜的性质（例如流动性），这对于大多数应用是理想的。我们使用中子反射率研究了氧化物表面电荷（通过改变 pH 值和离子强度）和二价 Ca(2+) 在控制二棕榈酰磷脂酰胆碱（DPPC）双层在蓝宝石（α-Al(2)O(3)）(11 ̅20)面上的表面覆盖和潜在堆叠中的作用。当蓝宝石表面带正电荷且离子强度低（I=15 mM NaCl）时，在低至中性 pH 值时形成几乎完全的双层。在更高的 pH 值接近蓝宝石等电点时，以及在更高的 I≥210 mM 或添加 2mM Ca(2+)时，覆盖率降低。后两种效应不是加性的，这表明 Ca(2+)减轻了高 I 的影响。这些趋势与通过吸附等温线确定的 α-Al(2)O(3)颗粒上磷脂吸附以及原子力显微镜确定的单晶（10 ̅10）蓝宝石上磷脂吸附的先前结果一致，表明氧化物表面化学依赖性效应在实验技术中的一致性。
