A diagnostic device is provided that includes a plurality of retainment regions, with the retainment regions that are separated by at least one dissolvable barrier. The retainment regions can be interconnected through at least one fluid processing passageway. A retainment region can include a container such as a retainment region, well, chamber, or other receptacle, or a retainment region such as a surface on which the material is retained. The retainment regions can include a reaction retainment region, one or more reagent retainment regions, each containing unreacted reagents, and a sample retainment region. A pressure-actuated valve can be positioned in each fluid processing passageway interconnecting the one or more reagent retainment regions with the respective intermediate retainment regions interposed between each of the one or more reagent retainment regions and the reaction retainment region. The dissolvable barrier can be a fluid flow modulator in the at least one fluid processing passageway.