Physical characterization of exosomes and other extracellular vesicles using surface-based sensing

Doctoral thesis, 2015

Extracellular vesicles (EVs) are hundred of nanometer sized particles secreted by almost all cell types. Exosomes are one type of EVs today intensively investigated due to the increased evidence suggesting that they play important roles as communicating vehicles in a broad range of physiological processes, pathological conditions and disease diagnostics. Their multifaceted profiles highlight the importance of elucidating how their different modes of biological action correlate with their biomolecular profiles, physicochemical properties and their concentration in biological fluids. This thesis explores the potential of two surface-based sensor methods, namely surface-plasmon resonance (SPR) and optical waveguide scattering / fluorescence microscopy (OWSFM), for physical characterization of EVs. EVs carrying specific exosomal marker were quantified in terms of bulk concentration using SPR. A key uncertainty of this quantification approach was suggested to originate from vesicles contraction upon adsorption to the sensor surface. This concern was scrutinized with dual-wavelength SPR, illustrating the advantage of dual-wavelength SPR over conventional SPR to quantify nanoparticle contraction in general and concentration determination of EVs in particular. As an extension of these findings, OWSFM was utilized to compare the optical density and lipid content of two sub-populations of extracellular vesicles observed at the single particle level in both scattering and fluorescence mode. In summary, the thesis work contributes with new tools for improved characterization of physicochemical properties of different EVs and concentration determinations of sub-population of EVs carrying exosomal markers.