Herceptin transcytosis into human breast cancer SK-BR-3 cells treated for 3 h promoted by Herceptin-functionalized gold nanoparticles (Her-GNP). Stains from left to right: anti-ErbB2 (Texas red), anti-transferrin receptor (Tfr) antibodies (FITC), and nuclear counterstain (DAPI). Vehicles from top to bottom: free Herceptin, 10 nm Her-GNP, and 40 nm Her-GNP. Each stain was overlaid in the fourth panel. The Her-GNP vehicles display enhanced cytosolic uptake of Herceptin, and the smaller 10 nm Her-GNP carriers demonstrate greater nuclear internalization than their 40 nm counterparts. Scale bars are 10 μM. Reproduced from [20]