A Microfluidic SERS Assay to Characterize the Phenotypic Heterogeneity in Cancer-Derived Small Extracellular Vesicles

Small extracellular vesicles (sEVs) are nanoscopic bioparticles that transport biomolecular cargoes between cells. sEVs have been implicated in many pathological processes such as cancer, rendering them as promising targets for therapeutics and diagnostics. Characterizing phenotypic differences in sEV biomolecular cargos could support understanding their roles in cancer. However, this is difficult due to similar physical properties of sEVs and requirement for highly sensitive analysis. Our method describes the preparation and operation of a microfluidic immunoassay with surface-enhanced Raman scattering (SERS) readouts, termed sEV subpopulation characterization platform (ESCP). ESCP applies an alternating current induced electrohydrodynamic flow to enhance collisions of sEVs with the antibody-functionalized sensor surface. Captured sEVs are labeled with plasmonic nanoparticles to facilitate multiplexed and highly sensitive phenotypic characterization of sEVs by SERS. ESCP is demonstrated for characterizing the expression of three tetraspanins (CD9, CD63, CD81) and four cancer-associated biomarkers (MCSP, MCAM, ErbB3, LNGFR) in sEVs derived from cancer cell lines and plasma samples.