Isolation and detection of exosomes via AAO membrane and QCM measurement

Increasing evidence suggests that exosomes are secreted by the majority of cancer cells and present in myriad biological fluids. They have been recognized as a potential new class of biomarkers for disease prognosis and diagnosis. The isolation and quantification of exosomes are crucial in facilitating exosome research. This paper presents a filtration method to isolate exosomes via anodic aluminum oxide (AAO) membrane and to quantify them using a quartz crystal microbalance (QCM). The filtration chip was designed to have two nano-porous AAO membranes sandwiched in between PDMS layers. In this study, fetal bovine serum (FBS) was adopted as the analyte for exosomal bioassays. The experimental results show that AAO membrane has a hydrophilic surface able to sieve exosomes by gravity. The spectrophotometric measurement and the result of gel electrophoresis confirmed that most of proteins in FBS were removed, leaving pure and undamaged exosomes for further analyses. Then, QCM measurement of the filtered FBS solution can give a quantitative analysis of exosome concentration. The relationship between the exosome concentration and its corresponding QCM's frequency shift is linear and monotonic. QCM is still sensitive to measure low concentration of exosomes.