In addition to the secondary and tertiary structure of a peptide, a further determinant for recognition is the immobilization of peptides to the solid phase used in an immunodiagnostic test. Antibody capture by peptides crucially depends on the accessibility of key residues and therefore the introduction of a spacer molecule to spatially separate the peptide from its carrier protein is vitally important [43] . The peptides in our study were synthesized with an N-terminal AHX-spacer coupled to biotin. The biotin was used to immobilize the peptide antigen to a streptavidin-coated solid phase, i.e. microscope glass slides and 96-well ELISA plates. Coating the biotinylated peptides to non-streptavidin surfaces such as Immulon 2HB (Thermo Scientific) or Poly Sorp (NUNC) ELISA plates, led in those samples tested to discrepancies of duplicate values and mostly reduced A 405nm values, in a non-linear manner (data not shown). Immobilization of peptides by direct adsorbance to the polystyrene surface might lead to sterical blockage of key residues necessary for interaction with antibodies and thus decrease the A 405nm values. Similarly, HIV-1 peptides showed in ELISA increased test sensitivity and specificity when immobilized via biotin-streptavidin [44] . Surfaces functionalized with streptavidin guarantee a directional, highly dense and reproducible coating of biotinylated peptide antigens. It has been shown that the direction of peptide immobilization is of secondary importance as long as peptides deriving from internal protein sequences are investigated [43] . Interactions of internal sequences do not depend on free N-or C-terminus and therefore attachment of spacer and carrier molecules can be achieved successfully at both termini of the peptide.