Multicolor Immunodiagnostic for Semiquantitative Visual Detection Syndrome Coronavirus 2 Specific Antibody: A Prospect Strategy for On-site COVID-19 Therapeutic Process Monitoring

Rapid detection of body fluid severe acute respiratory syndrome coronavirus 2(SARS-CoV-2) antibody is an effective strategy for infection therapeutic effect of coronavirus disease(COVID-19). Most detection methods require relatively large equipment, which limited their on-site application. Lateral flow immunoassay(LFIA) can be used to qualitative antibody detection based on the aggregation of gold nanoparticles (Au NPs), which exhibits just one-color change and cannot realize rapid quantitative detection without the help of additional equipment. In this study, a high-resolution multicolor colorimetric strategy was developed and applied to assessing antibody concentration at a glance based on etching of gold nanorods(Au NRs). Firstly, SARS-CoV-2 recombinant antigen was immobilized on the surface of the 96-wells. Then, horseradish peroxidase(HRP)-labeled second antibody combined with antibody to form an antigen-antibody-secondary antibody complex on the well surface, which has direct relationship with antibody concentration in the sample and can be used to oxidize 3, 3', 5, 5'-tetramethylbenzidine(TMB) to form TMB²⁺ at the presence of HRP. The generation of TMB²⁺ efficiently etch Au NRs to produce multicolor solution. The etching result in vivid color changes in the system has a relationship with the amount of SARS-CoV-2 IgM antibody. Under the optimal conditions, the proposed strategy exhibited a linear response in the 5.00―200 IU concentration range, and a detection limit of 1.29 IU for SARS-CoV-2 IgM antibody, with high sensitivity and specificity. This assay is prospective for the on-site semi-quantitative visual detection of SARS-CoV-2 IgM antibody concentration in the COVID-19 therapeutic process.