Determination of carcinoembryonic antigen in human sera by integrated beadbed immunoasay 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 o f colon cancer. Polystyrene beads precoated with anti-CEA antibody were int roduced into a microchannel, and then a serum sample containing CEA, the fi rst antibody, and the second antibody conjugated with colloidal gold were r eacted successively, The resulting antigen-antibodies complex, fixed on the bead surface, was detected using a thermal lens microscope (TLM). A highly elective and sensitive determination of an ultratrace amount of CEA in hum an 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 patien ts 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 similar to1%, thus shortening the overall analysis time from 45 h to 35 min. Moreover, troublesome operations requir ed for conventional heterogeneous immunoassays could be much simplified. Th is microchip-based diagnosis system is the first microchip-based system tha t is practically useful for clinical diagnoses with short analysis time, hi gh sensitivity, and easy procedures.