Assay methods

A method of detecting an exosome in a sample comprising:

• a binding the exosome to:
• (i) a capture reagent on a surface comprising the capture reagent for the exosome, wherein the surface also comprises an anchoring reagent comprising an anchoring oligonucleotide sequence complementary to an amplicon sequence;
• (ii) a first detection reagent for the exosome that is linked to a first nucleic acid probe;
• and (iii) a second detection reagent for the exosome that is linked to a second nucleic acid probe;
• thereby forming a complex on the surface comprising a binding reagent, the exosome and the first and second detection reagents;
• b using an extension process that requires the first nucleic acid probe and the second nucleic acid probe, extending the second probe to form an extended sequence comprising an anchoring oligonucleotide sequence complement that is complementary to the anchoring oligonucleotide sequence;
• c hybridizing the anchoring oligonucleotide sequence to the anchoring oligonucleotide sequence complement;
• and
• d measuring the amount of extended sequence bound to the surface.