ZnO Nanowire-Based Early Detection of SARS-CoV-2 Antibody Responses in Asymptomatic Patients with COVID-19

A serological immunoassay based on enzyme-linked immunosorbent assay (ELISA) is a crucial tool for screening and identification of human SARS-CoV-2 seroconversion. Various immunoassays are developed to detect the spike 1 (S1) and nucleocapsid (NP) proteins of SARS-CoV-2; however, these serological tests have low sensitivity. Here, a novel microplate (MP) is developed on which a ZnO nanowire (NW) is fabricated by a modified hydrothermal synthesis method. This plate is coated with SARS-CoV-2 NP and used as a fluorescent immunoassay (FIA) to detect antibodies specific for SARS-CoV-2 NP. Compared with the bare MP, the ZnO-NW MP binds high levels (up to 5 µg mL⁻¹) of SARS-CoV-2 NP tagged to histidine without any surface treatment. A novel serological assay based on the ZnO-NW MP is more sensitive than a commercial immunoassay, enabling early detection (within <5 days of a reverse transcription polymerase chain reaction-confirmed COVID-19 infection) of anti-SARS-CoV-2 NP IgG antibodies in asymptomatic patients with COVID-19. This is the first assay to detect early antibody responses to SARS-CoV-2 in asymptomatic patients. Therefore, this serological assay will facilitate accurate diagnosis of COVID-19, as well as estimation of COVID-19 prevalence and incidence.