WB was performed as we described previously (22 (link)). Briefly, the SARS-CoV-2-containing VGM or 40 μg/ml of the recombinant protein (SARS-CoV-2 S protein S1 subunit, S protein S2 subunit, or N protein) was mixed with an equal volume of the CuI dispersion or UPW. The CuI concentrations in the mixture were 0.38 and 3.8 mg/ml or 0 mg/ml (UPW group). At that time, 1.2 mg/ml NAC (Fujifilm Wako Pure Chemical Co.) was added to some mixtures to scavenge ROS. These mixtures were combined with sodium dodecyl sulfate (SDS) buffer with 2-mercaptoethanol (Fujifilm Wako Pure Chemical Co.) either immediately (0 h reaction time) or were agitated for 1.5, 3, 6, 12, or 24 h at 22°C to 25°C and 45% to 50% relative humidity prior to adding the SDS buffer (1.5, 3, 6, 12, or 24 h reaction time). The mixed samples were subjected to WB analyses.