A selective detection assay to determine the interaction between a cyclic oligopeptide and a target ligand, where the cyclic oligopeptide is an internally limited cyclic oligopeptide comprising a ring of at least six amino acids to specifically bind to a target ligand, where the ring comprises two amino acid domains, each domain comprising epitope-forming amino acids and two functional groups in association which are the side chains of the amino acids in association or the modified side chains of the amino acids or groups in association added to the side chain of the amino acid in association, where the functional groups in association are located so that they form one or more non-covalent intracyclic associations； whereby the cyclic oligopeptide is limited in a unique conformation so that epitope-forming amino acids form an epitope in each domain, each epitope being capable of specifically binding to a target ligand； and where the oligopeptide comprises two epitopes； and each functional group in association is a C8-C20 hydrocarbon chain that may be saturated or unsaturated, a linear chain or a branched and substituted or unsubstituted chain； and where the cyclic oligopeptide has the structure selected from the following structures: ** Formula ** where A, B, C, X, Y and Z represent the epitope-forming amino acids； A and X represent amino acids D and B, C, Y and Z represent amino acids L or A and X represent amino acids L and B, C, Y and Z represent amino acids D； an epitope with the A-B domain is formed and an epitope with the Z-X-Y domain is formed； and each Σ represents an amino acid in association； and ** Formula ** where, B, C, D, W, X, Y and Z represent the epitope-forming amino acids； an epitope with the D-C-A-B domain is formed and an epitope with the Z-X-Y-W domain is formed； and each Σ represents an amino acid in association.Un ensayo de detección selectiva para determinar la interacción entre un oligopéptido cíclico y un ligando diana, donde el oligopéptid
