Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale, Illinois 62901, United States.
Langmuir. 2012 Sep 11;28(36):12989-98. doi: 10.1021/la300724z. Epub 2012 Jul 16.
We investigate interactions between receptors and ligands at bilayer surface of polydiacetylene (PDA) liposomal nanoparticles using changes in electronic absorption spectroscopy and fluorescence resonance energy transfer (FRET). We study the effect of mode of linkage (covalent versus noncovalent) between the receptor and liposome bilayer. We also examine the effect of size-dependent interactions between liposome and analyte through electronic absorption and FRET responses. Glucose (receptor) molecules were either covalently or noncovalently attached at the bilayer of nanoparticles, and they provided selectivity for molecular interactions between glucose and glycoprotein ligands of E. coli. These interactions induced stress on conjugated PDA chain which resulted in changes (blue to red) in the absorption spectrum of PDA. The changes in electronic absorbance also led to changes in FRET efficiency between conjugated PDA chains (acceptor) and fluorophores (Sulphorhodamine-101) (donor) attached to the bilayer surface. Interestingly, we did not find significant differences in UV-vis and FRET responses for covalently and noncovalently bound glucose to liposomes following their interactions with E. coli. We attributed these results to close proximity of glucose receptor molecules to the liposome bilayer surface such that induced stress were similar in both the cases. We also found that PDA emission from direct excitation mechanism was ~2-10 times larger than that of the FRET-based response. These differences in emission signals were attributed to three major reasons: nonspecific interactions between E. coli and liposomes, size differences between analyte and liposomes, and a much higher PDA concentration with respect to sulforhodamine (SR-101). We have proposed a model to explain our experimental observations. Our fundamental studies reported here will help in enhancing our knowledge regarding interactions involved between soft particles at molecular levels.
我们使用电子吸收光谱和荧光共振能量转移（FRET）研究了聚二乙炔（PDA）脂质体纳米粒子双层表面上受体和配体之间的相互作用。我们研究了受体与脂质体双层之间连接方式（共价与非共价）的影响。我们还通过电子吸收和 FRET 响应研究了脂质体与分析物之间大小依赖性相互作用的影响。葡萄糖（受体）分子通过共价或非共价键附着在纳米粒子的双层上，它们提供了葡萄糖与大肠杆菌糖蛋白配体之间分子相互作用的选择性。这些相互作用在共轭 PDA 链上产生了应力，导致 PDA 的吸收光谱发生变化（从蓝色变为红色）。电子吸收的变化也导致了附着在双层表面上的共轭 PDA 链（受体）和荧光团（磺基罗丹明 101）（供体）之间的 FRET 效率的变化。有趣的是，我们发现与大肠杆菌相互作用后，共价和非共价结合的葡萄糖与脂质体的 UV-vis 和 FRET 响应没有明显差异。我们将这些结果归因于葡萄糖受体分子与脂质体双层表面的接近度，使得两种情况下的诱导应力相似。我们还发现，直接激发机制的 PDA 发射比基于 FRET 的响应大 2-10 倍。这些发射信号的差异归因于三个主要原因：大肠杆菌与脂质体之间的非特异性相互作用、分析物与脂质体之间的大小差异以及 PDA 相对于磺基罗丹明（SR-101）的浓度要高得多。我们提出了一个模型来解释我们的实验观察结果。我们在这里报告的基础研究将有助于提高我们对软粒子在分子水平上相互作用的认识。
