Confocal microscopy of skin treated for 8 hr with PEG, PEG-amine (NH2), or carboxylic acid (COOH)-coated quantum dots 565 (QD 565; spherical quantum dots with a core/shell diameter of 4.6 nm); coatings are noted at the top of each column. Top row: Confocal-differential interference contrast (DIC) channel only allows an unobstructed view of the skin layers. Middle row: Confocal-DIC overlay with the quantum dot fluorescence channel (green) shows quantum dot localization within the skin layers; arrows indicate the presence of quantum dots in the epidermis or dermis. Bottom row: Fluorescence intensity scan of quantum dot emission. Quantum dots 565 are localized in the epidermal (PEG and COOH coatings) or dermal (NH2 coating) layers by 8 hr; all scale bars (lower right corners) are 50 μm; reproduced with permission from Reference 15.