Abstract
Chemical analysis of small extracellular vesicles (sEVs) circulating in body fluids holds potentials in noninvasive diagnosis of diseases and evaluation of therapeutic treatments. However, quantification of sEVs remains a challenge due to lacking of cost-effective analytical protocols. Herein we report a facile method based on size exclusion chromatography with fluorescence detection (SEC-FD) for sEVs quantification. After removal of cells and cell debris, a 0.50 mL sample (e.g., cell culture medium) is incubated with CM-Dil dye to fluorescently label sEVs. The incubation solution is then separated on a SEC column packed with Sepharose CL-4B. The eluent is monitored fluorescently at Ex553 nm/Em570 nm by using a fluorometer equipped with a 50-μL flow through cuvette. Separation efficiency of the proposed SEC-FD method was evaluated by analyzing 100 nm liposomes and albumin-FITC conjugate. Liposomes were eluted out in less than 6 min, about 10 min before albumin-FITC. A separation repeatability (RSD in retention time) of 1.4% (n = 5) was obtained for liposomes. In analysis of cell culture media, linear calibration curves based on SEC-FD peak height versus sEVs concentration were obtained with r2 value of 0.996. Intraday quantification repeatability (RSD in peak height) was 3.2% (n = 5). The detection limit was estimated to be 2.9 × 107 exosome particles/mL. The proposed assay was applied to the first study of sEVs secretion from TK6 cells cultured in serum-free medium for a culturing period from 1 to 48 h.