Gold nanoparticle-based novel enhancement method for the development of highly sensitive immunochromatographic test strips

The immunochromatographic assay that is in widespread use for pregnancy diagnosis is a method for easy visual judging of the antigen-antibody reaction using gold nanoparticle. The rapid observation of results directly by the naked eye ensures the convenience of performing bioassays on-field. Therefore, gold nanoparticle-based immunochromatographic assays have provided attractive means for developing biosensors without the handling of toxic reagents, while allowing an easy and rapid procedure. However, the detection limit of this method is higher than the conventional method, enzyme-linked immunosorbent assay (ELISA). In this report, we developed a highly sensitive immunochromatographic assay for the detection of human chorionic gonadotropin hormone (hCG) as the model case. In this research, we are reporting the application of a new 'sensitizer' that contains gold nanoparticle conjugated primary antibody and the antigen. The sensitizer was added to the membrane after finishing the application of the normal method. The antigen of the sensitizer was captured by the secondary antibodies at the test line on the strip. As a result, the accumulation of the gold nanoparticle increased at the test line, and the sensitivity was higher. The sensitivity of our method could be enhanced by the sensitizer to almost the same level of ELISA assay. The test line intensity of hCG at 25 pg/ml treated with sensitizer was almost equal to the density that we observed at 1.0 ng/ml with the normal method. We also tested the performance of the sensitizer by using the surface plasmon resonance (SPR) technology of BIACORE™. The sensitizer using immunochromatographic assay is a promising candidate for decentralized diagnosis in clinically important fields such as the sensitive detection of cancer markers.