An array of peptide dimer ligand-binding capture agents for capturing an analyte in a sample wherein each of said ligand-binding capture agents comprises first and second peptide chains being formed as a dimer by means of a covalent link therebetween, wherein said covalent link has been formed by reaction of first and second thiol groups on said first and second peptides, each of said first and second peptide chains comprises a chain of between 5 and 25 amino acids wherein each amino acid is a D-enantiomer or an L-enantiomer, each of said first and second peptide chains have different amino acid sequences, said first peptide is immobilised via an attachment moiety to a substrate, said attachment moiety being selected from the group consisting of a hydrophobic moiety and a moiety forming a covalent bond with the substrate and wherein the first and second peptide chains have amino acid sequences which are combinatorially-varied and the array comprises discrete spatially addressable locations and each location comprises a different capture agent.