Fig. 2: Nanovaccine residence time in the nasal cavity and antigen biodistribution.

a In vivo fluorescence images of RBD biodistribution, comparing mice (n = 7–8/group) nasally instilled (10 µL) with a dose of 1) antigen alone (Ag, 20 µg/dose), 2) mucoadhesive polymer-coated Ag (MaP), 3) silica nanoparticle-carried Ag (SiNP), and 4) Ag loaded onto SiNP and functionalized by MaP (SiNP-MaP), along with control animals (non-immunized). The corresponding fluorescence intensity (FI) was measured in the animals at b 0 (T0), c 3 (T3), d 6 (T6), and e 24 h (T24) post-instillation, and f in the different organs, including heart (H), lung (LG), liver (LV), spleen (S), kidney (K), and brain (B), at 24 h post-nasal instillation. Data in (b–f) were represented as mean values ± SD and represent results from a single experiment. Differences between tested groups per time point or per organ were assessed using ANOVA followed by Tukey’s multiple comparison test (three or more groups) or Student’s t-test (two groups). P < 0.05 was considered statistically significant. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001. The * without an indicator means the group’s difference in relation to all others. Ag RBD antigen, SiNP silica-based nanoparticle, MaP mucoadhesive polymer, s second.