devices and methods for performing assays to determine the presence or quantity of a specific analyte of interest in a fluid sample . in devices according to this invention two separate flow paths are established sequentially in the device with a single user activation step . the first flow path delivers the analyte of interest and conjugate soluble binding reagents to the solid phase . if analyte is present , an analyte : conjugate complex is formed and immobilized . the volume of sample delivered by this first path is determined by the absorbent capacity of the solid phase , and not by the amount of sample added to the device , relieving the user from the necessity of measuring the sample . the sample / conjugate mixture is prevented from entering the second flow path because the capillarity and the surface energy of the second flow path prevent it from being wetted by this mixture . the second flow path allows a wash reagent to remove unbound conjugate and sample from the solid phase to the absorbant , and optionally to deliver detection reagents . the invention may be adapted to many assay formats including , sandwich immunoassays , colloidal gold , or sol particle assays , heterogeneous generic capture assays and competitive assays . in one embodiment , sandwich assays can be performed by immobilizing an analyte binding reagent on the solid phase , and drying a labeled analyte binding reagent in the first flow path . in a competitive assay embodiment , the first flow path would contain labeled analyte that is dissolved by the sample , and the analyte binding reagent is immobilized on the solid phase . in each of these embodiments , the assay can be further modified to run in a “ generic capture ” format , where the solid phase binding reagent is instead conjugated to a generic ligand such as biotin , and dried in the first flow path , and a generic ligand binding reagent is immobilized on the solid phase . another aspect of the present invention includes a subassembly for the immunoassay device that is comprised of a plastic housing and a means for delivering fluid and / or wash solution . this subassembly comprises a structure formed from a hydrophobic polymer selectively treated with a water insoluble surface active agent that has been applied as a solution in an organic solvent rendering portions of the surface hydrophilic . when the surface is contacted with an aqueous liquid , it flows only along the treated areas , creating a defined fluid flow path , thereby delivering sample / conjugate solutions to said solid phase .