Immunochromatography

Immunochromatography comprising:

• mixing an antigen-containable specimen and modified magnetic particles, which are magnetic particles modified with a substance having a specific affinity to the antigen, to obtain a mixture containing magnetic particle composite bodies which are composite bodies of the antigen and the modified magnetic particle;
• collecting magnetic particles in the mixture containing the magnetic particle composite bodies using magnetism;
• dissociating the modified magnetic particles from the magnetic particle composite body to obtain an antigen-concentrated solution by mixing the collected magnetic particles with a dissociation solution which is an alkaline or acidic solution, where an amount of the dissociation solution is smaller than the antigen-containable specimen in terms of mass ratio;
• neutralizing the antigen-concentrated solution using a neutralization solution to obtain a neutralized antigen-concentrated solution;
• spreading gold particle composite bodies on an insoluble carrier having a reaction site at which a second binding substance capable of binding to an antigen in the neutralized antigen-concentrated solution has been immobilized, in a state where the gold particle composite bodies which are composite bodies of the antigen and modified gold particles which are gold particles modified with a first binding substance capable of binding to the antigen are formed;
• capturing the gold particle composite bodies at the reaction site of the insoluble carrier;
• and
• silver-amplifying the gold particle composite body captured in the capturing step.