Abstract: An immunoassay apparatus on a chip is disclosed, which can quantitatively measure the concentration of hormones (particularly corticosterone and progesterone) in a biological sample. Such an apparatus can be designed to be used in the field, saving time and money for those taking the measurements. The measurements are made within a micro-fluidic channel configured on a substrate of a chip, which is loaded using simple capillary forces. Competitive immunoassay can be performed, with the competing agents being the hormone (e.g., antigen) and hormone-coated latex beads (e.g., both pre-mixed in a methanol solution).