Histologic evaluation of extravasation of each nanoparticle. Extravasation of single nanoparticles in mice with human tumor xenografts. (a, c, e) Hematoxylin and eosin-stained images observed by bright-field microscopy after injection of 40-, 100-, and 200-nm particles, respectively. (b, d, f) Laser confocal microscopy images after injection of 40-, 100-, and 200-nm particles, respectively. Particles of 40 nm (b) and 100 nm (d) extravasated (arrows), whereas 200-nm nanoparticles did not extravasate (arrow) (f). Scale bar, 10 μm.