Nanoparticle characterization. A) Scanning electronic microscopy of the BSA nanoparticles. B) Adsorption of DENV onto the surface of BSA nanoparticles. BSA nanoparticles were incubated with the tetravalent solution of inactivated DENV and later purified by three cycles of centrifugation. The presence of viral particles on the surface of NPs was demonstrated by ELISA assays using monoclonal antibodies against DENV-1, 2, 3 or 4. Bars represent the mean of data collected from three independent experiments.