Exosomes, first isolated 30 years ago, are nanoscale vesicles shed by most types of cells. The nucleic acid rich content of these nanoparticles, floating in virtually all bodily fluids, has great potential for non-invasive molecular diagnostics and may represent a novel therapeutic delivery system. However, current isolation techniques such as ultracentrifugation are not convenient and do not result in high purity isolation. This represents an interesting challenge for microfluidic technologies, from a cost-effective perspective as well as for enhanced purity capabilities, and point-of-care acquisition and diagnosis.
In this review, the authors present the current challenges, comment on the first microfluidic advances in this new field and propose a roadmap for future developments. This review enables biologists and clinicians familiar with exosome enrichment to assess the performance of novel microfluidic devices and, equally, enables microfluidic engineers to educate themselves about this new class of promising biomarker-rich particles and the challenges arising from their clinical use.
Ciliated structures for exosome isolation and capture by Wang et al. The hierarchical geometry of the device does not allow cells larger than 1 μm to access the wired area, due to the distance between the pillars (b) being too narrow (900 nm). Smaller cell debris can enter the micropillar area but are excluded by the ciliated nano structure (a), which forms pores with diameters ranging between 30 and 200 nm, in order to selectively trap exosomes and small EVs. Smaller proteins and molecules are free to pass through the device without being captured.