Using a Quartz Crystal Microbalance with dissipation monitoring, QCM-D (label-free system) measuring changes in resonant frequency (Delta f) that equate to mass deposited on a sensor, we showed the attachment, over a 60 min period, of a monolayer of PC3 cells to the gold electrodes of the quartz crystal sensor, which had been rendered hydrophilic. That MVs were released upon BzATP stimulation of cells was confirmed by NTA analysis (average 250 nm diameter), flow cytometry, showing high phosphatidylserine exposition and by fluorescent (Annexin V Alexa Fluor (R) 488-positive) and electron microscopy. Over a period of 1000s (16.7 min) during which early apoptosis increased from 4% plateauing at 10% and late apoptosis rose to 2%, the Delta f increased 20 Hz, thereupon remaining constant for the last 1000s of the experiment. Using the Sauerbrey equation, the loss in mass, which corresponded to the release of 2.36 x 10(6) MVs, was calculated to be 23 ng. We therefore estimated the mass of an MV to be 0.24 pg. With the deposition on the QCM-D of 3.5 x 10(7) MVs over 200s, the decrease in Delta f (Hz) gave an estimate of 0.235 pg per MV. (C) 2014 Elsevier Inc. All rights reserved.