Determination of Protein Amount in Nanosized Synthetic Liposomes by Surface Effect Raman Spectroscopy (SERS)

Abstract

Accurate characterization of synthetic liposomes is essential since they give information about the vesicular struc-tures in bodily fluids such as extracellular vesicles. The characterization tasks are generally the determination of the sizes of the liposomes and the profiling of the liposomes' content. Optical tweezers and Surface Enhanced Raman Spectroscopy (SERS) were used to profile the nanosized liposomes. The size distribution of the trapped liposomes (140 nm on average) was found by using Einstein's Brownian motion equation, consistent with the size distribution obtained from dynamic light scattering measurements. Besides, Gramicidin-encapsulated liposomes were measured using SERS, and statistically significant differentiation was found in Raman intensities between liposome populations with altering concentrations of proteins. This study uniquely measured size distributions of nano-sized liposomes with conventional optical tweezers (without plasmonics) and determined the chemical differ-ences between empty and protein encapsulated liposomes with high accuracy using Raman spectroscopy.