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Direct Exosome Analysis with “Single exosome per microliter” sensitivity

Following our long-standing collaboration with Yamauchi at UQ and Salomon Groups at UQCCR, we developed an extremely simple and inexpensive platform method for the direct isolation and quantification of exosomes.

Most of the current strategies for exosome isolation and quantification are time-consuming and largely dependent on pre-isolation step using a commercial extraction kit, which requires extensive sample manipulation, costly isolation, reagents, tedious procedures, and sophisticated equipment, and is prone to bias/artefacts. In our new method, a new class of gold-loaded ferric oxide nanocubes were initially functionalized with a generic tetraspanin (exosomes associated) antibody and dispersed in sample fluids where they work as ‘dispersible nanocarriers’ to capture bulk population of exosomes. After magnetic collection and purification, nanocubes-bound exosomes were transferred to the tissue-specific antibody-modified electrodes printed on plastic/ceramic substrates.

As a proof of principle, we used a specific placental marker, placenta alkaline phosphatase, to detect exosomes secreted from placental cells. The peroxidase-like activity of nanocubes was then used to accomplish an ELISA-based sensing protocol for naked-eye observation along with UV-visible and electrochemical detection of specific exosomes present in placental cell-conditioned media. We detected single exosome per microliter with the relative standard deviation of < 5.5 % without using the pre-isolation step with commercial “total exosome isolation kit”.

This method will find the application in quantifying specific populations of exosomes for various clinical applications including cancer and pregnancy complications.