One-step quantification of salivary exosomes based on combined aptamer recognition and quantum dot signal amplification.

As promising fluid biomarkers for non-invasive diagnosis, naturally-occurring exosomes in saliva have attracted a wide interest for their potential application in oral diseases especially oral cancers. However, accurate quantification of salivary exosomes is still challenging due to the current difficulties in simultaneous identification and measurement of these nano-sized vesicles. In this study, we developed a novel fluorescent biosensor for one-step sensitive quantification of salivary exosomes based on magnetic and fluorescent bio-probes (MFBPs). Within the MFBPs, self-assembled DNA concatamers loaded with numerous quantum dots (QDs) were ingeniously tethered to aptamers, which were anchored on the surface of magnetic microspheres (MMs). Efficient recognition and capture of an exosome by the aptamer would simultaneously trigger the release of a DNA concatamer as the detection signal carrier, thereby generating a "one exosome-numerous QDs" amplification effect. As the result, this biosensor allowed one-step quantification with less assay time and achieved a high sensitivity with low limit of detection. Moreover, unique fluorescent properties of QDs and the superparamagnetism of MMs offered a strong anti-interference ability, enabling a robust quantification in complex matrices. Furthermore, this biosensor exhibited a good clinical feasibility with favorable accuracy comparable to nanoscale flow cytometry, and a superiority in label-free analysis and convenient operation. This study provides a novel and general strategy for one-step sensitive quantification of exosomes from body fluids, facilitating the development of exosome-based liquid biopsy for disease diagnosis.