Patent ID: 7553675

Claim:
A test device for determining the presence or absence of an analyte in a fluid sample, the test device comprising a test strip comprising: a) a support bearing a mark thereon; b) one or more matrices in fluid flow contact with one another and positioned over the support, the one or more matrices comprising: i) a sample receiving zone for applying a fluid sample suspected of comprising an analyte, ii) a label zone comprising a detectable mobile labeled reagent selected to bind to the analyte, and iii) an observation area comprising a capture zone comprising an immobilized capture reagent, wherein the labeled reagent produces a detectable signal in the capture zone that is related to the presence of analyte in the sample, and wherein the observation area comprises a material that is opaque in a dry state and transparent in a moist state; and wherein the mark is detectable within the observation area when the observation area is in a moist state.