CD9 and cancer: The major benefits of the tool include: an attractive limit of detection of 3.7 × 105 particles/μL, small-volume samples, high sensitivity (slope of calibration curve) and specificity for determination of CD81+/CD9+ and EpCAM+/CD9+ EVs derived from HT29 and MDA-MB-231 cell culture supernatants, and accurate quantification of EVs isolated from complex biological fluids of cancer patients (serum, ascites).