Morphological changes in gold core–chitosan shell nanostructures at the interface with physiological media. In vitro and in vivo approach

•Chitosan easily adapts to pH changes reconstructing at the surface of AuNPs.•Chitosan offeres biocompatibility to AuNPs.•Polymeric shell allows the crossing of the blood–brain barrier.•AuNPs do not agglomerate inside the brain and have a good dispersion within tissue.•The polymeric coating did not degrade with pH increase.•Interaction between AuNPs inside brain tissues is limited in strength and abundance. Chitosan–gold nanoparticles (AuNPs) were prepared to investigate the behavior of such nanosystems at the interface with biological media. Microstructural characterization by Transmission Electron Microscopy, Atomic Force Microscopy, and Optical Microscopy was carried out in order to provide information regarding the morphology features and size distribution. In vivo studies showed no morphological changes within the brain tissue in rats after the administration of AuNPs. However, nanoparticles size distribution in the in vivo localized tissue areas indicated better dispersion than in the in vitro colloidal solution. Also the size of the AuNPs that reached the brain tissue seemed to decrease compared with their size in the colloidal solution. In order to understand the factors that contribute to the increase of AuNPs dispersion degree within the brain tissue, this study was focused on simulating the pH conditions from the hemato-encephalic medium. A theoretical model was also applied in order to correlate the intensity of the interaction between two AuNPs and their volume ratio to further explain the absence of the agglomerated AuNPs and their high degree of dispersion within the brain tissue.