Design of Lipid-Nanoparticle Assemblies for High-Sensitive Lipid Membrane Analysis

Metal nanoparticles are frequently utilized in biological sensing and analysis. Localized surface plasmon resonance (LSPR) properties is important to achieve higher efficiency of surface-enhanced Raman scattering (SERS), and AuNPs and silver nanoparticles have been studied and utilized for SERS studies. In biological systems, a lipid bilayer membrane plays important roles such as controlling the structure and location of membrane protein, transporting molecules via cell membranes, and maintaining homeostasis of cell. Thus, fundamentals of molecular behaviors in lipid bilayers are of interest to investigate the potential functions of biological membranes.

The aim of this study is to design SERS platforms for lipid membrane systems. Here, small (diameter: 5 nm) and large (diameter: 100 nm) diameter AuNPs were employed to induce membrane surface-enhancement Raman spectra. The SERS from AuNP_5nm@lipid and AuNP_100nm@lipid were compared as well as the enhancement factor (EF) values. The AuNP_5nm was successfully embedded in the inner lipid membrane due to the small size and hydrophobic property. Raman spectra of the AuNP_5nm@lipid showed that the signals of the fingerprint region were stronger than AuNP_100nm@lipid. The Raman spectrum from AuNP_5nm@lipid described the enhanced signals in the hydrophobic area which indicated that AuNP_5nm was entrapped in the lipid bilayer. Finally, the differentiate Raman spectra was also compared between AuNPs and lipid and it was concluded that AuNP_5nm@lipid has been exhibited enhanced peaks derived from hydrophobic region of the membrane. The cholesterol was also indicated that it was localized in the hot spot area of the AuNPs. This approach will shed lights in characterizing liquid-ordered vs liquid-disordered membrane phases, and in detecting the AuNP associated lipids in membrane systems.