Peptide libraries having enhanced subsequence diversity and methods for use thereof

A method for identifying a peptide binder, the method comprising:

• contacting a first sample with an engineered peptide library;
• selecting at least one of the plurality of peptides from the first subset of peptides;
• detecting a first signal output characteristic of an interaction of the sample with the engineered peptide library;
• and
• selecting the at least one peptide, which binds to the sample, based on the first signal output;
• wherein the engineered peptide library comprises:
• a plurality of peptide features, each of the peptide features including at least one peptide, the at least one peptide comprising a composite region having a defined sequence of amino acids of length N, the composite region representing k different elements, each of the different elements having defined sequence of amino acids of length x;
• wherein
• x, N and k are integers,
• x is less than N,
• k is at least 2 and is defined by the equation, k=N−x+1,
• a total number of different elements represented by the engineered peptide library is KEng,
• the number of peptide features included in the engineered peptide library is F, and
• KEng is at least 0.8*k*F.