ASSAY DEVICE

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. For each group, under conditions where the test region is wet and devoid of tagging particles the energised photodetector photocurrent that is produced is denoted i1, when the group emitter is the only emitter that is energised, and T2 when the emitter of another group is additionally energised. Cross-talk (C), is then represented by the black arrows, and is defined according to the equation: C=20 log10 (i1/(i2−i1)) C is arranged to be greater than about 20 dB for at least one group of the device.