The use of exosomes
for diagnostic and disease monitoring purposes
is becoming particularly appealing in biomedical research because
of the possibility to study directly in biological fluids some of
the features related to the organs from which exosomes originate.
A paradigmatic example are brain-derived exosomes that can be found
in plasma and used as a direct read-out of the status of the central
nervous system (CNS). Inspired by recent remarkable development of
plasmonic biosensors, we have designed a surface plasmon resonance
imaging (SPRi) assay that, taking advantage of the fact that exosome
size perfectly fits within the surface plasmon wave depth, allows
the detection of multiple exosome subpopulations of neural origin
directly in blood. By use of an array of antibodies, exosomes derived
from neurons and oligodendrocytes were isolated and detected with
good sensitivity. Subsequently, by injecting a second antibody on
the immobilized vesicles, we were able to quantify the amount of CD81
and GM1, membrane components of exosomes, on each subpopulation. In
this way, we have been able to demonstrate that they are not homogeneously
expressed but exhibit a variable abundance according to the exosome
cellular origin. These results confirm the extreme variability of
exosome composition and demonstrate how SPRi can provide an effective
tool for their characterization. Besides, our work paves the road
toward more precise clinical studies on the use of exosomes as potential
biomarkers of neurodegenerative diseases