Abstract: Colloidal gold, a marker widely embraced in commercial point-of-care testing (POCT) for immunochromatographic assays, is distinguished by its vivid color characteristics. It is environmentally benign, morphologically stable, and required no further visual modifications. This study details a straightforward process for fabricating test strips that obviate the need for sophisticated, costly equipment. Colloidal gold, synthesized by reducing the chloroauric acid with trisodium citrate, was conjugated to the nucleocapsid N protein antibody of SARS-CoV-2. With the test strip’s visible area, a competitive antibody-antigen-antibody sandwich complex forms, with the red test line serving as the basis for qualitative analysis of the virus. This detection approach is visually discernible, user-friendly, rapid (within 10 min), sensitive (detection limit of 0.5 ng∙mL⁻¹) and cost-effective (each strip costing no more than 5 yuan). The experimental process offers students an opportunity to engage with the specific biochemical reactions triggered by antigen-antibody interactions, fostering a deep interest in exploring rapid diagnostic technologies that integrate chemistry, biology, life sciences and nanomaterials.

Key words: Colloidal gold, Point-of-care testing (POCT), Immune chromatography, SARS-CoV-2 virus