STANDARD F COVID-19 Ag FIA

The rapid test STANDARD F COVID-19 Ag FIA (SD BIOSENSOR) was performed accordingly with the manufacturer’s instruction. It is an immunofluorescence lateral flow rapid test, where the samples react with an anti-nucleocapsid SARS-CoV-2 antibody; then, the fluorescence is read with an appropriate analyzer. Briefly, 350 μl of the sample was mixed with the extraction buffer and 4 drops were applied on the specimen well of the test device, and after 30 min, they were read at the STANDARD F200 analyzer. The cutoff index (COI) ≥ 1 was used to interpret the result as positive.

A previously isolated and quantified (in terms of plaque-forming unit-PFU/ml and viral copies/ml) SARS-CoV-2 was used to assess the detection limit of the kit, by performing a serial dilution of the virus (from 10¹² to 10³ viral copies/ml).