An excellent colorimetric aptasensor integrating multifunctional SNAs and TdT-induced dual signal amplification for rapid sensitive detection of exosomes

Exosome-based liquid biopsy has shown great potential in the diagnosis and prognosis of tumors, thus developing a convenient and reliable detection method is crucial for its clinical application. Herein, we construct a separable visual aptasensor for the sensitive detection of exosomes by using double spherical nucleic acids (DSNAs) and terminal deoxynucleotidyl transferase (TdT). In this system, CD63 aptamer-modified magnetic beads (MNPs-Apt CD63 , the first spherical nucleic acids) could efficiently capture exosomes, and avoid the aggregation of gold nanoparticles (GNPs) induced by complex components in the reaction system through magnetic separation. As the second spherical nucleic acids, abundant nucleolin aptamer-modified GNPs (GNPs-Apt nucleolin ) are used to specially identify exosomes. Then, those nucleolin aptamers can further produce long polyT sequences by the extension of TdT and induce polyA release from the GNPs-polyA (polyA-attached gold nanoparticles) by hybridization, thus resulting in the salt-induced aggregation of GNPs to produce color change for visual analysis of exosomes. Based on the above ingenious designed strategies, this method achieved a limit of detection (LOD) as low as 45 particles/μL, and showed accurate visual analysis for the clinical samples. We expect this method to provide a new opportunity for the exosomes-based point-of-care diagnosis of tumors.