Abstract: An assay device for the quantitative determination of the concentration of at least one analyte in a liquid sample. The device comprises a lateral flow membrane (46) comprising a plurality of test regions (41A, 41B) and formed from a light transmissive material, a plurality (44A, 44B) of planar organic light emitting diode (OLED) emitters comprising an emission layer of an organic electroluminescent material, and a plurality (49A, 49B) of planar organic photodetectors (OPDs) comprising an absorption layer of an organic photovoltaic material. Each test region comprises an immobilised component for retaining analyte tagging particles. Each test region is aligned with the emission layer of one emitter and the absorption layer of one photodetector. The aligned emitter, photodetector, and test region form a group such that the emitter is capable of illuminating the test region and the photodetector is capable of detecting light from the test region.

Abstract: An improved optical detection unit for an assay device, such as a lateral flow device, for the quantitative determination of the concentration of an analyte in a liquid sample, and an assay device comprising the same. The detection unit comprises an organic light emitting diode (OLED) emitter that has an emission spectrum E within the wavelength range from ?1 to ?2, and an organic photodiode detector (OPD) that has a light detection spectrum S within the wavelength range from ?1 to ?2. The detection unit has a test region that comprises a light absorbing component that has an absorbance spectrum A within the wavelength range from ?1 to ?2. The test region is positioned adjacent to the emitter and the detector to form an optical pathway from the light emitting diode to the photodiode through at least a portion of the test region. Formula M defines a relationship between E, S and A, and M is less than about 0.4.