Co-staining of vascular endothelial cells (ECs) with anti-CD31 antibody clearly revealed that many of the PS-L-IO/DiR nanoprobes co-localized with tumor vascular ECs, while many others infiltrated throughout extravascular tumor tissues (Figure 8c), further indicating the underlying mechanism for most of the PS-L-IO/DiR conjugates that bind specifically to the PS-exposed ECs and subsequently become internalized and eventually undergo transcytosis across the BBB. The gene discussed is PECAM1; the disease is neoplasm.