Graphene oxide nanoparticles (GO) loaded with VEGF by physical adsorption and conjugated to IR800, a commonly used near-infrared fluorescent dye, for VEGF delivery and imaging. (a) Schematic structure of IR800-VEGF-GO; (b) atomic force microscopy (AFM) images and (c) the height profile of IR800-GO (without VEGF); (d) absorption and (e) emission spectrum of various GO NPs. In vitro tube formation assay with (f) GO-IR800, (g) free VEGF, and (h) GO-IR800-VEGF, using human umbilical vascular endothelial cells (HUVECs). Reprinted from ref 36 with permission. Copyright 2013 Royal Society of Chemistry.