This study shows Flow Induced Dispersion Analysis (FIDA) working as a solution-phase method for characterising extracellular vesicles (EVs) and quantifying how antibodies bind to their surface. FIDA, an efficient, in-solution method for protein characterisation, was run on a Fida 1 instrument across three EV sources: engineered HEK vesicles displaying CD63-eGFP or a CD63-NeonGreen-Fc domain, and vesicles from immortalised mesenchymal stromal cells. Because the vesicles are never immobilised, a single measurement returns hydrodynamic size, population homogeneity and fluorescent labelling efficiency, and the same assay then follows antibody binding in real time as a shift in hydrodynamic radius, giving both epitope accessibility and the antibody concentration at which loading saturates. The authors position this as a route into EV standardisation and quality control, since surface interactions are read directly in suspension from small sample volumes. It is an example of using FIDA to size extracellular vesicles and to quantify antibody binding and epitope accessibility on their surface in solution.

From the same group, the poster Engineering Galectin-1 Valency to Promote Glycan-Dependent MSC-EV Association applies the same in-solution approach to lectin binding on mesenchymal stem cell vesicles.