A point-of-care selenium nanoparticle-based test for the combined detection of anti-SARS-CoV-2 IgM and IgG in human serum and blood

COVID-19 is a widespread and highly contagious disease in the human population. COVID-19 is caused by SARS-CoV-2 infection. There is still a great demand for point-of-care tests for detection, epidemic prevention and epidemiological investigation, both now and after the epidemic. We present a lateral flow immunoassay kit based on a selenium nanoparticle-modified SARS-CoV-2 nucleoprotein, which detects anti-SARS-CoV-2 IgM and anti-SARS-CoV-2 IgG in human serum, and the results can be read by the naked eye in 10 minutes. We expressed and purified the SARS-CoV-2 nucleoprotein in HEK293 cells, with a purity of 98.14% and a concentration of 5 mg mL(-1). Selenium nanoparticles were synthesized by l-ascorbic acid reduction of seleninic acid at room temperature. After conjugation with the nucleoprotein, a lateral flow kit was successfully prepared. The IgM and IgG detection limits of the lateral flow kit reached 20 ng mL(-1) and 5 ng mL(-1), respectively, in human serum. A clinical study sample comprising 90 COVID-19-diagnosed patients and 263 non-infected controls was used to demonstrate a sensitivity and specificity of 93.33% and 97.34%, respectively, based on RT-PCR and clinical results. No cross-reactions with rheumatoid factor and positive serum for anti-nuclear antibodies, influenza A, and influenza B were observed. Moreover, the lateral flow kit remained stable after storage for 30 days at 37 degrees C. Our results demonstrate that the selenium nanoparticle lateral flow kit can conveniently, rapidly, and sensitively detect anti-SARS-CoV-2 IgM and IgG in human serum and blood; it can also be suitable for the epidemiological investigation of COVID-19.