(510e) Characterization of Extracellular Vesicles By Atomic Force Microscopy

Exosomes and
other extracellular vesicles (EVs) are molecular
complexes consisting of a lipid membrane vesicle, its surface decoration by membrane
proteins and other molecules, and diverse luminal content inherited from a
parent cell, which includes RNAs, proteins, and DNAs. The characterization of
the hydrodynamic sizes of EVs, which depends on the size of the vesicle and its
coronal layer formed by surface decorations, has become routine. For exosomes,
the smallest of EVs, the relative difference between the hydrodynamic and
vesicles sizes is significant. The characterization of vesicles sizes by the cryogenic
transmission electron microscopy (cryo-TEM) imaging,
a gold standard technique, remains a challenge due to the cost of the
instrument, the expertise required to perform the sample preparation, imaging
and data analysis, and a small number of particles often observed in images. A
widely available and accessible alternative is the atomic force microscopy
(AFM), which can produce versatile data on three-dimensional geometry, size,
and other biophysical properties of extracellular vesicles. In this
presentation we guide the users in utilizing this analytical tool and outlines
the workflow for the analysis of EVs by the AFM, which includes the sample
preparation for imaging EVs in hydrated or desiccated form, the electrostatic
immobilization of vesicles on a substrate, data acquisition, its analysis, and
interpretation. The representative results (Figure 1) demonstrate that the fixation
of EVs on the modified mica surface is predictable, customizable, and allows
the user to obtain sizing results for a large number of vesicles. The vesicle
sizing based on the AFM data was found to be consistent with the cryo-TEM imaging (Figure 2).