Abstract: Provided is an immunochromatographic diagnostic kit which renders prompt diagnosis possible, has high analysis sensitivity, and gives test results with excellent reproducibility. The immunochromatographic diagnostic kit includes: a conjugate pad that contains a conjugate containing chromogenic particles which have an average particle diameter of 100-1,000 nm and attain a color intensity of 1.0-10.0, 10-90 wt % of the particles being derived from cellulose and 90-10 wt % of the particles being derived from a colorant; and a sample pad for an in vitro diagnostic reagent, the sample pad being constituted of nonwoven fabric that has a basis weight of 10-150 g/m2 and a thickness of 0.07-1.00 mm and comprises regenerated cellulosic fibers.

Abstract: Provided are an immunochromatography kit that is highly sensitive and capable of multicoloration, and organic colored microparticles that are ideal as an element of the immunochromatography kit. Organic colored microparticles having an average grain size between 10 and 1,000 nm and a color intensity between 1.0 and 5.0 are prepared using cellulose as the starting material. When the organic colored microparticles are used as a label in an immunochromatography kit, the immunochromatography kit is of a high sensitivity than conventional technology. The immunochromatography kit is also capable of multicoloration and is useful for rapid diagnosis.