An integrated lab-on-a-chip platform for pre-concentration and detection of colorectal cancer exosomes using anti-CD63 aptamer as a recognition element

Colorectal cancer (CC) is one of the common causes of cancer-related deaths around the globe. Identification of a novel biomarker for CC is of paramount importance for early diagnostics and reducing its mortality. Among the most promising biomarker candidates, exosomes hold great potential for cancer diagnosis, management, and treatment. Exosomes are extracellular vesicles secreted from cells and they contribute to the intercellular communication, immune response and the pathogenesis of many diseases including cardiovascular diseases, neurodegenerative diseases, and cancer. Several methods have been developed/utilized for exosome isolation and purification. However, these methods are time-consuming and have low purification efficiency. In this work, we developed the "apta-magnetic biosensor" platform for isolation, purification and detection of exosomes from cell culture. Anti-CD63 aptamer, which is conjugated to the surface of magnetic nanobeads, was used as a recognition element. A dynamic separation system was used which employs a transverse magnetic field along a microfluidic channel. The channel was exposed to an alternate magnetic field which imposes alternate magnetic force onto the magnetic bead-exosome complex. The combination of the fluid flow and magnetic force generates several "alternate trapping and releasing" events under continuous-flow conditions with each event representing a washing cycle. The graphene coated onto the surface of the magnetic nanobeads was used as a quencher for the fluorescently labeled aptamer (OFF state) in the absence of the target. Upon the addition of CD63 target protein, the aptamer dissociates from the graphene and binds to the target hence increasing the fluorescence intensity (ON state). A calibration plot of variable concentrations of exosomes vs fluorescence intensity was obtained and the detection limit was calculated as 1457 particles/mL. The specificity of the sensor was tested using closely associated proteins. The results showed that the aptamagnetic isolation, pre-concentration of exosomes and quantification demonstrate great potential for various clinical applications.