Rapid Naked-Eye Detection of a Liver Disease Biomarker by Discovering Its Monoclonal Antibody to Functionalize Engineered Red-Colored Bacteria Probes.

Glycocholic acid (GCA) is a biomarker for liver diseases, but few facile naked-eye detection methods have been reported to detect it till now. To tackle this challenge, we first prepared a novel monoclonal mouse antibody (mAb) of GCA by a hybridoma technique. The anti-GCA mAb exhibited high specificity, making its cross-reactivity with seven structurally and functionally related GCA analogs negligible. Using this anti-GCA mAb and an engineered red-colored bacterial strain (, ), we developed a simple naked-eye visualized method for GCA detection. Toward this goal, bacteria were turned red by 5-cyano-2,3-ditolyl tetrazolium chloride treatment and heat treated to an unculturable state, rendering the bacteria as an optical detection probe powerful in diagnostics. Through the natural binding ability of protein A on the surface of and the Fc fragment of a mouse antibody, the anti-GCA antibody was simply conjugated onto . Then, the engineered served as a red-colored bioprobe for detecting GCA through a coagglutination test. In the presence of GCA, the bioprobes aggregated into dense red-colored eye-visible clusters, enabling the sensitive detection of GCA with a concentration of 0.05-0.10 μg/mL. This naked-eye visualization method only takes a few minutes to detect GCA and avoids the use of expensive equipment. It represents a rapid, convenient, and simple method for detecting GCA to diagnose liver diseases.