ASSAY DEVICE

An assay device for the quantitative determination of the concentration of at least one analyte in a liquid sample comprises a planar emitter (2), a planar detector (3), a lateral flow membrane (4) interposed between the emitter (2) and the detector (3), a conjugate pad (5) in fluid communication with a proximal end of the lateral flow membrane (4), the conjugate pad (5) comprising optically detectable tagging particles bound to a first assay component, a sample pad (6) in fluid communication with the conjugate pad (5) and arranged to receive the liquid sample, and a wicking pad (7) in fluid communication with a distal end of the lateral flow membrane (4). The lateral flow membrane (4) is formed from a light transmissive material and is capable of transporting fluid from the conjugate pad (5) to the wicking pad (7) by capillary action. The lateral flow membrane (4) comprises at least one test region (8, 12) comprising an immobilised second assay component for retaining the tagging particles in the test region (8, 12) in dependence on the binding between the analyte, the first assay component and the second assay component in order to generate a concentration of tagging particles in the test region (8, 12) that is indicative of the concentration of the analyte in the liquid sample. The emitter (2) comprises an emission layer (9, 16) of an organic electroluminescent material and the emission layer (9, 16) is aligned with the test region (8, 12) of the lateral flow membrane 4, whereby the emitter (2) is capable of illuminating the test region (8, 12). The detector (3) comprises an absorption layer (10, 15) of an organic photovoltaic material and the absorption layer (10, 15) is aligned with the test region (8, 12) of the lateral flow membrane 4, whereby the detector (3) is capable of detecting light from the test region (8, 12).