Assay methods

1. 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.

2. The method of claim 1 wherein the capture reagent is an antibody, antigen, ligand, receptor, oligonucleotide, hapten, epitope, mimitope, or an aptamer.

3. The method of claim 1 wherein the first detection reagent is an antibody, antigen, ligand, receptor, oligonucleotide, hapten, epitope, mimitope, or an aptamer.

4. The method of claim 1 wherein the second detection reagent is an antibody, antigen, ligand, receptor, oligonucleotide, hapten, epitope, mimitope, or an aptamer.

5. The method of claim 1 , wherein the capture reagent and the first and second detection reagents are antibodies to a target molecule in or on the surface of the exosome.

6. The method of claim 5 wherein the capture reagent binds a common exosome target protein selected from CD9, CD63, CD81, Hsp70, PDCD6IP or Tsg101.

7. The method of claim 5 wherein at least one of the first or second detection reagents are antibodies to a disease-specific target molecule in or on the surface of the exosome.

8. The method of claim 1 wherein the first and second detection reagents each bind to interacting exosome target molecules.

9. The method of claim 8 wherein the interacting target molecules comprise a ligand-receptor pair and/or an mRNA molecule and an RNA binding protein.

10. The method of claim 1 wherein the extended sequence further comprises one or more detection sequences and the measuring step further comprises contacting the extended sequence with a plurality of labeled probes complementary to the one or more detection sequences.

11. The method of claim 1 wherein the extending step comprises binding the second probe to a template nucleic acid sequence, forming a circular nucleic acid template, and extending the circular template by rolling circle amplification.

12. The method of claim 1 wherein the extended probe remains localized on the surface following probe extension.

13. The method of claim 12 wherein the complex remains bound to the surface after the extending step.

14. The method of claim 12 wherein the extended probe is bound to the anchoring reagent at a position within 10-100 urn of the location of the complex on the surface.

15. The method of claim 1 wherein the extending step comprises PCR (Polymerase Chain Reaction), LCR (Ligase Chain Reaction), SDA (Strand Displacement Amplification), 3SR (Self-Sustained Synthetic Reaction), or isothermal amplification methods.

16. The method of claim 15 wherein the extending step comprises an isothermal amplification method.

17. The method of claim 16 wherein the isothermal amplification method is helicase-dependent amplification or rolling circle amplification (RCA).

18. The method of claim 1 wherein the extension process comprises contacting the complex formed in step (a) with a connector sequence comprising (i) an interior sequence complementary to the second probe and (ii) two end sequences complementary to non-overlapping regions of the first probe.

19. The method of claim 18 further comprising ligating the two end sequences of the connector oligonucleotide to form a circular target sequence that is hybridized to both the first and second probes.

20. The method of claim 1 wherein the extension process comprises contacting the complex formed in step (a) with a first connector oligonucleotide sequence including a first connector probe sequence complementary to a first region of the first probe and a first region on the second probe, and a second connector oligonucleotide comprising a second probe sequence complementary to a second non-overlapping region of the first probe and a second non-overlapping region of the second probe.