Spectroscopic characterization of nanovesicles originating from self-forming synthetic PEGylated lipids

Abstract

In this study, we have utilized the advantages of biophotonics and nanotechnology in conjunction with vibrational spectroscopic techniques to understand the various properties of biological macromolecules known as lipid bilayers or liposomes and nanovesicles. Liposomes are spherical particles that can encapsulate a fraction of the solvent into their interior. Liposomes are constructed of polar lipids which are characterized by having a lipophilic and hydrophilic group on the same molecules. Liposomes are nowadays used extensively as a model for biological membranes as well as drug and gene delivery vehicles. Here, we have studied newly developed novel self-forming synthetic PEGylated lipids (trademarked as QuSomes) and nanovesicles by means of Raman vibrational spectroscopic techniques. In contrast to conventional phospholipids, these new kinds of lipids spontaneously form liposomes or lipid vesicles upon hydration, without the supply of external activation energy. In addition, scanning electron microscopy (SEM) has been used for the imaging of single lipid vesicle and fluorescence correlation spectroscopy (FCS) has been utilized to measure the size distribution of such nanoparticles in suspensions. Furthermore, we have obtained an excellent signal-to-noise ratio in the Raman spectra for single particle of ∼100 nm dimension. The cross-sections of associated Raman signal for the lipid vesicles in PBS suspension have been estimated to be of the order of 10 −28 cm 2/(nanoparticles sr). In this work, we have found that the Raman spectra of PEGylated lipids are dominated by vibrational bands arising mainly from C–H and C–C stretching modes that have been used to identify important fingerprint regions. These spectra have been studied extensively as a function of temperature, pH value and size distribution of such nanoparticles to unravel the structural changes and conformational order and disorder phenomena.