In a polymer assay cartridge having wells containing reagents, beads and sample, where the wells are covered (e.g., with Parafilm® or films) and shipped to the point of care, the reagents and well contents can leak out. The reagent solutions are made semi-solid by adding hydrogel reagents and cooling to form a gel. Preferably, the hydrogel is heated before an assay is conducted with the cartridge, and pigmented beads in the wells indicate melting or excessive heating, or congealing of the hydrogel, based on pigment color change.