Measurements, applications, and impact of the refractive index of extracellular vesicles
||E. van der Pol|
||Scientific and Standardization Committee meeting of the International Society on Thrombosis and Haemostasis, Milwaukee, United States|
||June 26, 2014|
||Milwaukee 2014 Impact vesicle refractive index.pdf (1,452 kB)|
Vesicles are often studied by methods that detect light scattering, such as flow cytometry and nanoparticle tracking analysis (NTA). The amount of light scattered by a vesicle depends on its size and refractive index (RI). Consequently, knowledge of the RI is required to determine the vesicle size and provide insight in the smallest detectable vesicles. We have measured the diameter and light scattering of vesicles and beads by tracking their Brownian motion with NTA (NS500, Nanosight Ltd). We analytically described the relation between the diameter, RI, and light scattering of beads using Mie theory to determine the RI of vesicles from cell-free human urine. The mean refractive index of urine vesicles was 1.37, which is in agreement with preliminary results from others.
We used the most recent knowledge on the RI of vesicles to discuss recent achievements and insights in the optical detection of vesicles, including swarm detection, flow cytometry calibration, and the detection limit of NTA and Raman microspectroscopy. Furthermore, we hypothesized that the RI may provide a novel label-free parameter to distinguish vesicles from protein aggregates.