Determination of protein amount in nanosized synthetic liposomes by Surface Enhanced Raman Spectroscopy (SERS)

Accurate characterization of synthetic liposomes is essential since they give information about the vesic ular structures in bodily fluids such as extracellular vesicles. The characterization tasks are generally the determina tion 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 lip osomes (140 nm on average) was found by using Einstein's Brownian motion equation, consistent with the size dis tribution 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 differences between empty and protein encapsulated liposomes with high accuracy using Raman spectroscopy.