Abstract: The present invention, in some embodiments thereof, generally relates to methods and devices for determining the health status of a subject, e.g., whether the subject has a disease or other condition. In some embodiments, a plurality or mixture of species may be differentially solubilized in a single two-phase aqueous system, or other multi-phase aqueous system. The nature or degree of the solubilization of the species may be used to determine the health status of a subject. For example, some embodiments are directed to devices and methods for determining a disease or other condition as a function of the changes to the structure of two or more species. The species may be selected based on their differential solubility behavior in a two-phase or other multi-phase aqueous system.