Abstract: A bioassay, which is a segregative phase separation system (SPSS) where a bioassay signal intensifier is presented. The bioassay signal intensifier is an aqueous two-phase system (ATPS) component that causes the signal to intensify in one aqueous phase of a plurality of phases formed from the bioassay composition. The source of the signal resulting from the inclusion of a test sample is selectively partitioned into one phase that can be of significantly lesser volume than in the bioassay absent the bioassay signal intensifier, such the signal's source is concentrated in that phase, and the signal is intensified.