(a) The summary of AuNCs elimination routes from brain is schematically illustrated. The detail procedures of (I) to (IV) are shown in planar graphs and their captions. (b) The glymphatic system stimulated by CSF and AQP4 water channel continuously drained free AuNCs in parenchyma, drove them from capillary basement membrane to arterial basement membrane in tunica media for IPAD (I). The microglia could phagocytose and delivery AuNCs to the glymphatic system for promotion (II). (c) Free AuNCs in parenchyma was accessible to BBB and actively transported across BBB by endocytosis and exocytosis in exosomes (III). The microglia could secrete AuNCs in exosomes to further fuse with endothelia cells, facilitating the transcellular transport (IV).