The present invention discloses an affinity-binding
assay comprising a particle having at least four copies of a target molecule and at least two binding molecules specific for the target molecule, wherein a first of the binding molecules is associated with a first
label and a second of the binding molecules is associated with a second
label, wherein a particle having the first
label and a particle having the second label are distinguishable from a particle having both the first and second labels, wherein the first and second binding molecules each comprise at least two binding regions specific for the target molecule. The present invention also discloses a composition comprising a first binding molecule associated with a first label and a second binding molecule associated with a second label, wherein the
signal obtained from the first and second labels is distinguishable from the combined
signal of the first and second labels, characterized in that the first and second binding molecules each comprise at least two binding regions specific for essentially the same target molecule, preferably for essentially the same
epitope on the target molecule and a method for selecting a
synthetic antigen from a collection of at least three antigens comprising using the disclosed composition and method. The invention further discloses an
antigen obtainable by the above-described method and capable of inducing an early immune response, a kit of parts to perform the method, the use of antigens selected by the methods for use as a vaccine, and the use of antibodies and antigens as a medicament.