Fig. 3. Humoral antibody responses elicited by the pEr-P³-RBD nanovaccine.

The humoral antibody responses were detected using the pGOLD nanoplasmonic platform and pseudoviral neutralization antibody assay. (A) Note that RBD (WT)/RBD (Omicron) antigens were printed on the surface of pGOLD (62). Anti-RBD in the mouse serum are first captured by the assay and the labeled with anti-mouse IgG-infrared fluorescent dye (IgG-IRDye800). Binding between IgG with antigens is evaluated by reading the fluorescence intensities of IRDye800. (B) Quantitative anti-RBD (WT) IgG levels and (C) anti-RBD (Omicron) IgG levels in the serum of the mice vaccinated with RBD (WT) antigen-only, pEr-P³-RBD (WT), and pEr-P³-RBD (Omicron BA.1) without any adjuvant. The serum was collected on day 14, day 35, day 56, and day 235. Each point represents an individual animal. Error bars represent the SD of 10 (day 14, day 35, and day 56) or 5 (day 235) repeated experiments. Data are presented as mean values ± SD. (D) Log NT₅₀ for the neutralizing antibody levels against the WT SARS-CoV-2 pseudovirus and (E) Omicron BA.1 SARS-CoV-2 pseudovirus in the serum of the mice vaccinated with RBD (WT) antigens, pEr-P³-RBD (WT), and pEr-P³-RBD (Omicron BA.1) without any adjuvants. Each dose of the vaccine contains 10 μg of RBD antigens. Note that, in (D) and (E), each point represents the NT₅₀ titer measured with an individual animal. Error bars represent the SD of 10 (day 14, day 35, and day 56) or 5 (day 235) repeated experiments. The NT₅₀ of 1:100 dilution is set as the limit of quantitation (LOQ).