Characterization of Extracellular Vesicles by Sulfophosphovanillin Colorimetric Assay and Raman Spectroscopy

Abstract

Background: Detailed characterization of extracellular vesicles (EVs) is crucial for their application in medical diagnostics. However, the complexity of their chemical composition and the heterogeneity of EV populations make their characterization challenging. Here we describe two analytical procedures that can help overcome this challenge. Methods: Small EVs were isolated from conditioned cell culture media using ultracentrifugation and characterized using nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM). Raman spectroscopy was used to assess the overall composition of the isolated samples and lipids extracted from them. Sulfophosphovanillin (SPV) colorimetric assay was used to quantify the contents of lipid. Results: Six samples of EVs were characterized. The lipid contents measured using SPV assay was in reasonable agreement with the quantitative estimates based on the particle size and concentration measured using NTA. The most peaks observed in the Raman spectra could be attributed to either proteins or lipids, and their origins was confirmed by lipid extraction. The protein-to-lipid ratio was estimated based on the Raman spectra. Conclusions: The experiential procedures described in this study will help to overcome the challenge of quick and highly informative characterization of the EVs.

Keywords

• extracellular vesicles
• optical measurement
• lipid concentration
• optical assay
• raman spectroscopy