Determination of carcinoembryonic antigen in human sera by integrated bead-bed immunoassay in a microchip for cancer diagnosis

A bead-bed immunoassay system was structured on a microchip and applied to determine carcinoembryonic antigen (CEA), which is a commonly used marker of colon cancer. Polystyrene beads precoated with anti-CEA antibody were introduced into a microchannel, and then a serum sample containing CEA, the first antibody, and the second antibody conjugated with colloidal gold were reacted successively. The resulting antigen-antibodies complex, fixed on the bead surface, was detected using a thermal lens microscope (TLM). A highly selective and sensitive determination of an ultratrace amount of CEA in human sera was made possible by a sandwich immunoassay system that needs three antibodies for an assay. A detection limit dozens of times lower than the conventional ELISA was achieved. Moreover, when serum samples for 13 patients were assayed with this system, there was a high correlation (r = 0.917) with the conventional ELISA. The integration reduced the time necessary for the antigen-antibody reaction to approximately 1%, thus shortening the overall analysis time from 45 h to 35 min. Moreover, troublesome operations required for conventional heterogeneous immunoassays could be much simplified. This microchip-based diagnosis system is the first microchip-based system that is practically useful for clinical diagnoses with short analysis time, high sensitivity, and easy procedures.