ImmunoInertial microfluidics: A novel strategy for isolation of small EV subpopulations

Cancer-specific small extracellular vesicles (sEVs), known as exosomes, have shown a great promise to serve as novel biomarkers for cancer diagnosis and prognosis in liquid biopsies. However, the high heterogeneity of sEVs posed great technical challenges to acquiring their molecular information. A simple and reproducible method for isolating subpopulations of sEVs can significantly enhance the detection and stratification of these circulating biomarkers and their function. This study used the synergic effects of the immunoaffinity-based approach and inertial microfluidics (ImmunoInertial microfluidics) to isolate specific subpopulations of sEVs. At first, the cancer cell-derived sEVs were captured on microbeads of varying sizes which were functionalized with specific capture antibodies such as epithelial cell adhesion molecule (EpCAM), epidermal growth factor receptor (EGFR), and the programmed death-ligand 1 (PD-L1), facilitating the selective capture of sEVs. The sEVs-bearing microbeads were subsequently introduced to a series of inertial microfluidic channels, called iZExoSub (inertial zigzag microfluidics for exosome subpopulation separation), for size-based bead separation. Results revealed more than 90% efficiency in sEVs subpopulation separation, further proved via flow cytometry analysis data. Our approach is capable of selective isolation and quantitative detection of important biomarkers from sEVs subpopulations with high sensitivity and low cost and has the capacity to process samples of varying volumes, ranging from µL up to mL continuously. This system can outperform FACS machines in terms of sample throughput by orders of magnitudes. In addition, this study emphasized the necessity of using a consistent sEV marker (as capture and detector) across different samples for accurate assessment of subpopulations.