Development of an aptasensor for electrochemical detection of exosomes

Exosomes are small (50-100 nm in diameter) vesicles secreted from various mammalian cells. Exosomes have been correlated with tumor antigens and anti-tumor immune responses and may represent cancer biomarkers. Herein, we report on the development of an aptamer-based electrochemical biosensor for quantitative detection of exosomes. Aptamers specific to exosome transmembrane protein CD63 were immobilized onto gold electrode surfaces and incorporated into a microfluidic system. Probing strands pre-labeled with redox moieties were hybridized onto aptamer molecules anchored on the electrode surface. In the presence of exosomes these beacons released probing strands with redox reporters causing electrochemical signal to decrease. These biosensors could be used to detect as few as 1 × 10⁶ particles/mL of exosomes, which represents 100-fold decrease in the limit of detection compared to commercial immunoassays relying on anti-CD63 antibodies. Given the importance of exosome-mediated signal transmission among cells, our study may represent an important step towards development of a simple biosensor that detects exosomes without washing or labeling steps in complex media.