Capture agents and related compositions, methods and systems

1. A multi-ligand capture agent comprising

a first five to eighty amino acid polypeptide ligand, a second five to seven amino acid polypeptide ligand and a third five to seven amino acid polypeptide ligand,

wherein the first polypeptide ligand and second polypeptide ligand are bound to each other by a first triazole linkage,

wherein the second polypeptide ligand and third polypeptide ligand are bound to each other by a second triazole linkage,

wherein in isolation the first polypeptide ligand can bind a target,

wherein in isolation the second and third polypeptide ligands can bind the target,

wherein the first, second and third polypeptide ligands bind to distinct portions of the target,

wherein the multi-ligand capture agent can specifically bind the target,

wherein the first, second and third polypeptide ligands contact the target when the multi-ligand capture agent binds the target and

wherein each of the amino acids in the first, second and third ligands is a D-amino acid or glycine.

2. The multi-ligand capture agent of claim 1 , wherein the first polypeptide ligand comprises a formula of x 1 x 2 x 3 x 4 x 5 x 6 , wherein x 1 , x 2 , x 3 , x 4 ,x 5 and x 6 are selected from D-arginine, D-histidine, D-lysine, D-aspartic acid, D-glutamic acid, D-serine, D-threonine, D-asparagine, D-glutamine, glycine, D-proline, D-alanine, D-valine, D-isoleucine, D-leucine, D-methionine, D-phenylalanine, D-tyrosine and D-tryptophan and wherein the second polypeptide ligand comprises a formula of x 7 x 8 x 9 x 10 x 11 x 12 , wherein x 7 , x 8 , x 9 , x 10 , x 11 and x 12 are selected from the group consisting of D-lysine, D-leucine, D-tryptophan, D-phenylalanine, D-isoleucine, glycine and D-valine.

3. The multi-ligand capture agent of claim 1 , wherein the first polypeptide ligand or the second polypeptide ligand comprise amino acid sequences selected from the group consisting of kfwlkl, kwlwGl and nlivfr.

4. The multi-ligand capture agent of claim 1 , wherein the third polypeptide ligand comprises an amino acid sequences selected from the group consisting of kfwlkl, kwlwGl and nlivfr.

5. The multi-ligand capture agent of claim 3 , wherein the first polypeptide ligand comprises an amino acid sequence of kfwlkl.

6. The multi-ligand capture agent of claim 3 , wherein second polypeptide ligand comprises an amino acid sequence of kwlwGl.

7. The multi-ligand capture agent of claim 4 , wherein third polypeptide ligand comprises an amino acid sequence of nlivfr.

8. The multi-ligand capture agent of claim 1 , further comprising a fourth polypeptide ligand.

9. The multi-ligand capture agent of claim 8 , wherein the fourth polypeptide ligand comprises a formula of x 19 x 20 x 21 x 22 x 23 x 24 , wherein x 19 , x 20 , x 21 , x 22 , x 23 and x 24 are selected from D-arginine, D-histidine, D-lysine, D-aspartic acid, D-glutamic acid, D-serine, D-threonine, D-asparagine, D-glutamine, glycine, D-proline, D-alanine, D-valine, D-isoleucine, D-leucine, D-methionine, D-phenylalanine, D-tyrosine and D-tryptophan.

10. The multi-ligand capture agent of claim 1 , wherein at least one polypeptide ligand comprises at least one L-amino acid.

11. The multi-ligand capture agent of claim 1 , wherein the capture agent further comprises an additional molecule or functional group attached to the capture agent which produces a desired chemical or biological activity.

12. The multi-ligand capture agent of claim 11 , wherein the desired chemical or biological activity is solubility, stability, bioavailability, immunogenicity, detectability, and reactivity.

13. The multi-ligand capture agent of claim 11 , wherein the additional molecule or functional group is a hydrophilic compound, a hydrophobic compound, a carrier or a label.

14. The multi-ligand capture agent of claim 13 , wherein the label is selected from the group consisting of radioactive isotopes, radioactive dyes, fluorophores, fluorescent dyes, absorbent dyes, chemiluminescent dyes, chromophores, enzymes, enzyme substrates, enzyme cofactors, enzyme inhibitors, dyes, metal ions, nanoparticles, and metal sols.

15. The multi-ligand capture agent of claim 13 , wherein the label is selected from the group consisting of biotin, avidin, streptavidin and haptens.

16. The multi-ligand capture agent of claim 1 , wherein each triazole linkage has a structure selected from:

wherein R 1 and R 2 are linkers.

17. The multi-ligand capture agent of claim 16 , wherein the triazole linkage is Tz1 or Tz2.

18. The multi-ligand capture agent of claim 1 , wherein the first polypeptide ligand comprises an N-terminus, a C-terminus and a plurality of side chains.

19. The multi-ligand capture agent of claim 18 , wherein the first polypeptide ligand is bonded to the first triazole linkage at the N-terminus.

20. The multi-ligand capture agent of claim 18 , wherein the first polypeptide ligand is bonded to the first triazole linkage at the C-terminus.

21. The multi-ligand capture agent of claim 18 , wherein the first polypeptide ligand is bonded to the first triazole linkage at one of the side chains.

22. The multi-ligand capture agent of claim 1 , wherein the second polypeptide ligand comprises an N-terminus, a C-terminus and a plurality of side chains.

23. The multi-ligand capture agent of claim 22 , wherein the second polypeptide ligand is bonded to the first triazole linkage at the N-terminus.

24. The multi-ligand capture agent of claim 22 , wherein the second polypeptide ligand is bonded to the first triazole linkage at the C-terminus.

25. The multi-ligand capture agent of claim 22 , wherein the second polypeptide ligand is bonded to the first triazole linkage at one of the side chains.

26. The multi-ligand capture agent of claim 1 , wherein the third polypeptide ligand comprises an N-terminus, a C-terminus and a plurality of side chains.

27. The multi-ligand capture agent of claim 26 , wherein the third polypeptide ligand is bonded to the second triazole linkage at the N-terminus.

28. The multi-ligand capture agent of claim 26 , wherein the third polypeptide ligand is bonded to the second triazole linkage at the C-terminus.

29. The multi-ligand capture agent of claim 26 , wherein the third polypeptide ligand is bonded to the second triazole linkage at one of the side chains.