Abstract: Assays where harsh sample pretreatment for releasing an analyte is required are routinely performed in two separate vessels or on two physically separate surfaces. The present invention provides for the preparation of a surface suitable for performing assays where sample pretreatment is necessary. The appropriate surface is coated with a molecule coupled to biotin wherein the resulting surface is resistant to the analyte releasing step. It can then be overcoated with avidin. Treatment of samples with strong alkali and reducing agents to release complexed or bound analyte molecules prior to assay can be carried out in the presence of the coated surface without significantly reducing its binding activity. In this way, pretreatment and assay can be accomplished on the same surface or in the same reaction vessel.