Patent US 4,094,647

Test device for determining a characteristic of a sample, particularly for determining substances in fluid samples. The device comprises a strip element which is composed of a material capable of transporting a developing fluid therealong by capillarity and which has a portion at a predetermined location on the strip element for receiving the test sample and portions at predetermined locations on the strip element incorporated with reagent means for providing a detectable response sensitive to the characteristic under determination. The beginning end portion of the strip element is immersed in the developing fluid which, as a result, traverses the length of the strip element, thereby promoting appropriate contact between the test sample and the reagent means resulting in the disposition of a detectable response at a predetermined location on the strip element, which response is a function of the characteristic under determination. The test device is particularly suited for performing binding assays, in particular those wherein a radioisotope is used as a label, such as radioimmunoassays.