Label-free optical antibody testing kit based on a self-assembled whispering-gallery-mode microsphere.

The appearance of antibodies in blood is a critical signal to suggest the infection. A rapid and accurate detection method for the antibody is significant to the disease diagnosis, especially for the epidemic. To this end, a highly sensitive whispering-gallery-mode (WGM) optical testing kit is designed and fabricated for detecting the specific immunoglobulin antibodies. The key component of the kit is a silica self-assembled microsphere decorated with the nucleocapsid proteins (N-proteins) of the SARS-CoV-2 virus. After the N-protein antibody immunoglobulin G (N-IgG) and immunoglobulin M (N-IgM) solutions being injected into the kit, the WGM red-shifts due to the antigen-antibody reaction. The wavelength displacement rates are proportional to the concentrations of these two antibodies from 1 to 100 μg/mL. A good specificity of the kit is demonstrated by the nonspecific human immunoglobulin G (H-IgG) and immunoglobulin M (H-IgM).