Magnetophoretic slider assay for electrochemical detection of SARS-cov-2 nucleocapsid protein in nasal swab samples.

The COVID-19 pandemic highlighted the need for rapid and sensitive diagnostic tools. In this work, the Magnetophoretic Slider Assay (MeSA) was integrated with electrochemical detection (eMeSA) using screen-printed carbon electrodes for the first time for the detection of SARS-CoV-2 nucleocapsid protein (NP). A sandwich enzyme-linked immunosorbent assay (ELISA) was performed on streptavidin-labeled magnetic beads (MBs). The streptavidin MB/biotinylated antibody/NP complexes were added into the sample inlet, where the beads were trapped using an external magnet while the solution rehydrated the HRP-labeled antibody (HRP-Ab) and 3,3',5,5'-tetramethylbenzidine (TMB) pads. By sliding the external magnet along the channel, the bead complexes were moved to the reservoir under the HRP-Ab pad, forming sandwich complexes. These complexes were subsequently moved back across the device to reach the electrochemical detection zone, where they reacted with released TMB, which underwent oxidation upon reacting with HRP attached to the detection antibody, followed by reduction due to the voltage applied to the working electrode (0.0 V vs. Ag reference electrode). The assay showed promising results in detecting SARS-CoV-2 in 10 min, with a limit of detection of 8.89 ng/mL NP and 78.02 PFU/mL inactivated virus. The results from 15 human samples demonstrated 100% clinical specificity and 100% clinical sensitivity for samples with RT-PCR cycle threshold (C) values from 19 to 30, meeting WHO criteria for COVID-19 diagnostics. The eMeSA offers an alternative to traditional ELISA for a wide range of point-of-care and point-of-need diagnostic applications.