The present invention refers to an aqueous solution for use as medium for the specific binding reaction of a binding pair, wherein a first binding member recognizes its complementary second binding member. The solution contains a) a buffer to control pH; b) a compound A selected from a compound defined by the general formula I R1—[[CR2R3]P—O]q—R4, wherein R1 is hydrogen or hydroxy group, R2 for each unit independently is hydrogen or hydroxy group, R3 is hydrogen, methyl group, or ethyl group, R4 is hydrogen or alkyl group, p is an integer of from 2 to 10 and q is an integer of from 1 to 100, with the proviso that the compound at least carries two hydroxy groups; a polyol; or saccharide; and c) a non-ionic detergent.