Antigen detection method using sandwich immunoassay method

An antigen detection method, using sandwich immunoassay, the antigen detection method comprising:

• a first reaction step including, in a sensor chip which comprises a reaction zone where an antigen-capturing antibody is immobilized within a fine flow channel, a liquid discharge/suction section on an upstream side of the fine flow channel, and a liquid-mixing section on a downstream side of the fine flow channel, wherein the liquid-mixing section has a special form configured to generate turbulence in the liquid mixing section, feeding a sample liquid containing a target antigen into the fine flow channel to the reaction zone of the sensor chip so as to allow the antigen-capturing antibody to capture the target antigen;
• a second reaction step including feeding a labeling liquid containing a labeling antibody into the fine flow channel to the reaction zone so as to label the target antigen captured by the antigen-capturing antibody, after the first reaction step;
• and
• a signal measurement step including measuring a signal obtained from the labeling antibody used to label the target antigen in the second reaction step,
• wherein:
• in the first reaction step, when the sample liquid containing the target antigen is fed to the reaction zone, the sample liquid is fed, via the fine flow channel, until the sample liquid reaches the liquid-mixing section arranged on the downstream side of the fine flow channel, and
• in the second reaction step, when the labeling liquid is fed to the reaction zone where the target antigen has been captured by the antigen-capturing antibody, the labeling liquid is fed, via the fine flow channel, in such a manner that the labeling liquid does not reach the liquid-mixing section arranged on the downstream side of the fine flow channel.