Quantum clots (QDs) are rapidly emerging as an important class of nanoparticles (NPs) with potential applications in medicine However, little is known about penetration of QDs through human skin This study investigated skin penetration of QDs in both in vivo and in vitro human skin Using the tape stripping method, this study demonstrates for the first time that QDs can actually penetrate through the stratum corneum (SC) of human skin Transmission electron microscope (TEM) and energy diverse X-ray (EDX) analysis showed accumulation of QDs in the SC of a human skin equivalent model (HSEM) after dermal exposure to QDs These findings suggest possible transdermal absorption of QDs after dermal exposure over a relatively long period of time (C) 2010 Elsevier Inc All rights reserved