A molecular trap to reduce free-hapten interference in an assay, the molecular trap comprising: a molecular structure soluble in an aqueous assay solution to selectively bind free-hapten, the molecular structure comprising a molecular cage that comprises a shell that surrounds a cavity having characteristics to selectively capture and retain a hapten that is unconjugated or free in the assay solution and a modified specific binding partner (sbp) to the free-hapten, wherein the free-hapten in the aqueous assay solution is free biotin, the shell is selected from the group consisting of a cyclodextrin shell and a molecularly imprinted polymer shell that specifically binds the hapten, the modified sbp to free biotin is one of a modified streptavidin, a modified avidin and traptavidin and comprises one or both of a dextran aldehyde and a steric hindering polymer, the modified sbp having slower specific free-hapten binding off-rate characteristics than other free-hapten specific binding partners (sbps) assay reagents, wherein the molecular cage further comprises a coating on the shell, the coating comprising one or more of a selectively permeable material for the free-hapten, an ionic charge to one or both of attract the free-hapten and repel other assay molecules in the assay solution, and a polarity to facilitate one or both of selective retention of the free-hapten and steric repellence of the other assay molecules in the assay solution, wherein the coating comprises one or more of proteins or peptides, dextran aldehyde or amino dextran, ethylenediamine, tetra-ethylene penta-amine, an ionically charged moiety, and a hydrophobic moiety. a molecular structure soluble in an aqueous assay solution to selectively bind free-hapten, the molecular structure comprising a molecular cage that comprises a shell that surrounds a cavity having characteristics to selectively capture and retain a hapten that is unconjugated or free in the assay solution and a modified specific binding partner (sbp) to the free-hapten, wherein the free-hapten in the aqueous assay solution is free biotin, the shell is selected from the group consisting of a cyclodextrin shell and a molecularly imprinted polymer shell that specifically binds the hapten, the modified sbp to free biotin is one of a modified streptavidin, a modified avidin and traptavidin and comprises one or both of a dextran aldehyde and a steric hindering polymer, the modified sbp having slower specific free-hapten binding off-rate characteristics than other free-hapten specific binding partners (sbps) assay reagents, wherein the molecular cage further comprises a coating on the shell, the coating comprising one or more of a selectively permeable material for the free-hapten, an ionic charge to one or both of attract the free-hapten and repel other assay molecules in the assay solution, and a polarity to facilitate one or both of selective retention of the free-hapten and steric repellence of the other assay molecules in the assay solution, wherein the coating comprises one or more of proteins or peptides, dextran aldehyde or amino dextran, ethylenediamine, tetra-ethylene penta-amine, an ionically charged moiety, and a hydrophobic moiety.