Departamento de Física, Química e Biologia, Faculdade de Ciências e Tecnologia, UNESP, 19060-900 Presidente Prudente, SP, Brazil.
Langmuir. 2009 Nov 17;25(22):13062-70. doi: 10.1021/la901923v.
The use of phospholipids as mimetic systems for studies involving the cell membrane is a well-known approach. In this context, the Langmuir and Langmuir-Blodgett (LB) methods are among the main techniques used to produce ordered layers of phospholipids structured as mono- or bilayers on water subphase and solid substrates. However, the difficulties of producing multilayer LB films of phospholipids restrict the application of this technique depending on the sensitivity of the experimental analysis to be conducted. Here, an alternative approach is used to produce LB films containing multilayers of the negative phospholipid dipalmitoylphosphatidylglycerol (DPPG). Inspired by the electrostatic layer-by-layer (LbL) technique, DPPG multilayer LB films were produced by transferring the DPPG Langmuir monolayers from the water subphase containing low concentrations of the cationic polyelectrolyte poly(allylamine hydrochloride) (PAH) onto solid substrates. Fourier transform infrared (FTIR) absorption spectroscopy revealed that the interactions between the NH(3)(+) (PAH) and PO(4)(-) (DPPG) groups might be the main driving forces that allow growth of these LB films. Besides, ultraviolet-visible (UV-vis) absorption spectroscopy showed that the multilayer LB films can be grown in a controlled way in terms of thickness at nanometer scale. Cyclic voltammetry showed that DPPG and PAH are more packed in the LB than LbL films. The latter finding is related to the distinct molecular architecture of the films since DPPG is structured as monolayers in the LB films and multilamellar vesicles in the LbL films. Despite the interaction with PAH, cyclic voltammetry also showed that DPPG retains its biological activity in LB films, which is a key factor since this makes DPPG a suitable material in sensing applications. Therefore, multilayer LB films were deposited onto Pt interdigitated electrodes forming sensing units, which were applied in the detection of a phenothiazine compound [methylene blue (MB)] using impedance spectroscopy. The performance of DPPG in single-layer and multilayer LB films was compared to the performance of sensing unities composed of DPPG in single-layer and multilayer LbL films, showing the importance of both the thickness and the molecular architecture of the thin films. As found in a previous work for LbL films, the high sensitivity reached by these sensing units is intimately related to changes in the morphology of the film as evidenced by the micro-Raman technique. Finally, the interaction between MB and the (DPPG+PAH) LB films was complemented by pi-A isotherms and surface-enhanced resonance Raman scattering (SERRS).
将磷脂用作研究细胞膜的模拟系统是一种众所周知的方法。在这种情况下，Langmuir 和 Langmuir-Blodgett (LB) 方法是主要用于在水亚相和固体基底上产生单层或双层结构的磷脂有序层的技术之一。然而，由于对要进行的实验分析的敏感性，生产多层 LB 磷脂膜的困难限制了该技术的应用。在这里，使用一种替代方法来生产含有负磷脂二棕榈酰磷脂酰甘油 (DPPG) 的多层 LB 膜。受静电层层 (LbL) 技术的启发，通过将 DPPG Langmuir 单层从含有低浓度阳离子聚电解质盐酸聚烯丙胺 (PAH) 的水亚相转移到固体基底上来制备 DPPG 多层 LB 膜。傅里叶变换红外 (FTIR) 吸收光谱表明，NH(3)(+) (PAH) 和 PO(4)(-) (DPPG) 基团之间的相互作用可能是允许这些 LB 膜生长的主要驱动力。此外，紫外可见 (UV-vis) 吸收光谱表明，多层 LB 膜可以在纳米级厚度上以可控的方式生长。循环伏安法表明，DPPG 和 PAH 在 LB 中比 LbL 膜更紧密地堆积。后一种发现与膜的不同分子结构有关，因为 DPPG 在 LB 膜中呈单层结构，而在 LbL 膜中呈多层囊泡结构。尽管与 PAH 相互作用，但循环伏安法也表明 DPPG 在 LB 膜中保留其生物活性，这是一个关键因素，因为这使得 DPPG 成为传感应用中的一种合适材料。因此，将多层 LB 膜沉积到形成传感单元的 Pt 叉指电极上，将其应用于使用阻抗谱检测吩噻嗪化合物 [亚甲蓝 (MB)]。与由单层和多层 LbL 膜中的 DPPG 组成的传感单元相比，比较了 DPPG 在单层和多层 LB 膜中的性能，这表明薄膜的厚度和分子结构都很重要。如先前对 LbL 膜的研究发现，这些传感单元达到的高灵敏度与薄膜形貌的变化密切相关，这一点可以通过微拉曼技术得到证明。最后，通过 π-A 等温线和表面增强共振拉曼散射 (SERRS) 补充了 MB 与 (DPPG+PAH) LB 膜之间的相互作用。
