Abstract: An assay card and devices and methods for isolating chambers on the assay card are described. The assay card comprises a substrate formed of one or more materials, e.g., plastic, having a softening temperature, the substrate defining channels communicating with respective reaction chambers. The assay card may be heated in a region of the channels to at least the softening temperature. The softened plastic may be deformed, e.g., with a tool which may or may not also provide the heat for softening the substrate. In this manner, the plastic of the substrate may be caused to at least partially obstruct the channels, thereby isolating the reaction chambers. The invention also relates to a method of manufacturing a tool device that includes pins for heating and deforming an assay card.