Light-induced acceleration of specific binding between CEACAM-5 and antibodies for early detection of colorectal cancer.

Immunoassay methods such as enzyme-linked immunosorbent assay using antigen-antibody reactions have been applied to detect biomarker proteins in the case of various diseases (e.g., cancer). However, these methods comprise several-hour-long pre-treatment processes (incubation and washing) before detection, and their sensitivity is limited by the affinity of protein and antibody sets. Here, we demonstrate the rapid and highly sensitive analysis of a cancer biomarker at several hundreds of attograms using a microflow-type light-induced acceleration system (MF-LAC-SYS) to enhance the reaction between the multiple antibodies and glycoprotein (CEACAM-5) from human plasma containing multiple impurities with the help of theoretical analysis. Adjusting the surface charge of the antibody-modified beads and buffer solution components, we could detect pg mL-1 levels of CEACAM-5 at high sensitivity under a laser beam irradiation of several hundred mW for several minutes at a defocused condition equivalent to the microchannel width. Specifically, we discovered the existence of nanoscale CEACAM-5 aggregates related to the sensitivity of the MF-LAC-SYS, using dynamic light scattering and electron microscopy. The results will potentially pave the way for a platform using unconventional immunoassays for liquid biopsy and blood proteomics.