Digital Detection of Exosomes by Interferometric Imaging

Exosomes, which are membranous nanovesicles, are actively released by cells and have been attributed to roles in cell-cell communication, cancer metastasis, and early disease diagnostics. The small size (30-100 nm) along with low refractive index contrast of exosomes makes direct characterization and phenotypical classification very difficult. In this work researchers from Nexgen Arrays and Boston University present a method based on Single Particle Interferometric Reflectance Imaging Sensor (SP-IRIS) that allows multiplexed phenotyping and digital counting of various populations of individual exosomes (>50 nm) captured on a microarray-based solid phase chip. They demonstrate these characterization concepts using purified exosomes from a HEK 293 cell culture. As a demonstration of clinical utility, the researchers characterize exosomes directly from human cerebrospinal fluid (hCSF). Their interferometric imaging method could capture, from a very small hCSF volume (20 uL), nanoparticles that have a size compatible with exosomes, using antibodies directed against tetraspanins. With this unprecedented capability, the researchers foresee revolutionary implications in the clinical field with improvements in diagnosis and stratification of patients affected by different disorders.

Schematic representation of the SP-IRIS detection process

(A) SP-IRIS detection principle, monochromatic LED light illuminates the sensor surface and the interferometriclly enhanced nanoparticle scattering signature is captured on a CMOS camera. (B) Demonstrates SP-IRIS signal for polystyrene nanoparticles with a diameter from 50–200 nm which can be used to infer size of captured EVs. (C) Image of the SP-IRIS chip. (D) Low-magnification interferometric image showing microarray of immobilized capture probes. (E) SP-IRIS image of a capture probe. NVDX analysis software recognize capture spot and detects nanoparticles captured.