In situ chemical patterning

1. An in situ synthesized pseudo random peptide library for use in an immunosignature assay, wherein synthesis of the pseudo random peptide library uses a minimum number of patterned steps to construct the pseudo random peptide library on a substrate, wherein the minimum number of patterned steps (M) is less than the product of the number of different monomer units (R) and the length of the peptide (N) according to

M<R×N,

comprising:

a) determining the minimum number of patterned steps (M), wherein the minimum number of patterned steps (M) is at least 33% of the number of patterned steps needed to construct an uncorrelated set of sequences in the pseudo random peptide library, wherein the peptide library is disease agnostic;

b) assigning an activated or inactivated designation to each feature of a patterned step;

c) assigning a monomer to each feature that is designated as activated; and

d) coupling the monomers at each feature on the substrate that is designated as activated; wherein the monomers are sequentially coupled for the minimum number of patterned steps of (a), thereby providing a pseudo-random array for use in the immunosignature assay.

2. The pseudo random peptide library of claim 1 , wherein said synthesis is photolithography-based.

3. The pseudo random peptide library of claim 2 , wherein the photolithography-based synthesis comprises a photomask pattern step.

4. The pseudo random peptide library of claim 3 , wherein the photomasking step photomasks a feature of about 0.5 micron to about 200 microns in diameter and a center-to-center distance of about 1 micron to about 300 microns on center.

5. The pseudo random peptide library of claim 3 , wherein the number of photomasks needed to construct the peptide library is about 33% to about 95% of the number of photomasks needed to construct a peptide library with an uncorrelated set of sequences.

6. The pseudo random peptide library of claim 3 , wherein the number of photomasks needed to construct the peptide library is about 51% to about 75% of the number of photomasks needed to construct a peptide library with an uncorrelated set of sequences.

7. The pseudo random peptide library of claim 3 , wherein the number of photomasks needed to construct the peptide library is about 51% to about 55% of the number of photomasks needed to construct a peptide library with an uncorrelated set of sequences.

8. The pseudo random peptide library of claim 3 , wherein each feature on each photomask is randomly assigned an activated or inactivated designation.

9. The pseudo random peptide library of claim 1 , wherein the library comprises at least 10,000 features on the substrate.

10. The pseudo random peptide library of claim 1 , wherein the library comprises at least 100,000 features on the substrate.

11. The pseudo random peptide library of claim 1 , wherein the library comprises at least 330,000 features on the substrate.

12. The pseudo random peptide library of claim 1 , wherein the library comprises at least 1,000,000 features on the substrate.

13. The pseudo random peptide library of claim 1 , wherein the substrate is selected from the group consisting of arrays, wafers, slides, and beads.

14. The pseudo random peptide library of claim 1 , wherein the peptides are about 5 amino acids to about 25 amino acids in length.

15. The pseudo random peptide library of claim 14 , wherein the peptide lengths are not uniform between features.

16. The pseudo random peptide library of claim 1 , wherein amino acids C, I, T, and M, and optionally Q and E, are not included as amino acids available during peptide synthesis.

17. The pseudo random peptide library of claim 1 , wherein the activated designation is clear.

18. The pseudo random peptide library of claim 1 , wherein the inactivated designation is opaque.

19. The pseudo random peptide library of claim 1 , wherein the coupling of the monomers at each feature forms a linear or a branched structure.