(A) Representation of ProSNAs crossing an in vitro BBB model. Cells were treated with fluorescently labeled proteins on the apical side of a transwell insert. (B) Normalized fluorescence readings of the basolateral side were taken periodically and plotted to measure the protein’s transcytosis efficiency. Each point represents the mean of n =4 measurements, the error bars show SD, and the line is a nonlinear regression fit graphed using GraphPad Prism. (C) Explicit fluorescence significance comparison after 90 minutes incubation of either Dextran 70 kDa, β-Gal-AF647, TfR ProSNA or Scr ProSNA. The statistical significance was analyzed using ordinary one-way ANOVA, followed by tukey multiple comparison. **** p-value < 0.0001, *** p < 0.001, ** p < 0.01, and * p < 0.05.