Improving capture efficiency of human cancer cell derived exosomes with nanostructured metal organic framework functionalized beads

Abstract Extracellular vesicles (EVs) have emerged as an invaluable tool for analyzing the physiological processes and an alternative source of disease diagnostic and prognostic biomarkers in liquid biopsies. Exosomes are a subset of EVs offer a window into altered cellular or tissue states, and their detection potentially offers a multicomponent early-stage diagnostic readout. Immunocapture and flow cytometry analysis of exosomes using micron-sized beads has been reported to be a reproducible technique for analysis of exosome surface markers. Nevertheless, the capture capacity remains poor due to limited available surface area. In this study, we have proposed a nanocoating strategy using metal-organic framework (MOF) materials, in particular, Zeolitic Imidazolate Framework-8 (ZIF-8), for highly efficient capturing of low concentration of exosomes from minimally processed samples. In this method, a ZIF-8 thin film was formed on polydopamine-polyethyleneimine (PDA-PEI) coated polystyrene microbeads to improve antibody immobilization due to the larger surface area provided by the MOF microstructures. This novel coating enabled us to detect as little as 50 exosomes per 10 µm polystyrene bead functionalized with ZIF-8/PDA-PEI, which is 180 times higher than the previously reported methods using naked microbeads. This coating requires a lower concentration of antibody to capture exosomes on the surface of microbeads compared to the standard protocols. More importantly, the higher concentration of exosomes on each bead surface provides the opportunity (i.e., higher signal intensity) to sort the beads using fluorescence-activated cell sorting, facilitating molecular analysis of post fractionation exosomes. Additionally, the exosomes can easily be detached from the coated microbeads using EDTA, limiting the usage of harsh chemicals. The procedure described here can be easily reproduced and employed regardless of the biological sample used to obtain exosomes.