Assessment of Quantum Dot Penetration into Skin in Different Species Under Different Mechanical Actions

Abstract

Skin penetration is one of the major routes of exposure fornanoparticles to gain access to a biological system. QD nanoparticleshave received a great deal of attention due to their fluorescentcharacteristics and potential use in medical applications. However,little is known about their permeability in skin. This study focuses onthree types of quantum dots (QD) with different surface coatings andconcentrations on their ability to penetrate skin. QD621 (polyethyleneglycol coated, PEG) was studied for 24 h in porcine skin flow-throughdiffusion cells. QD565 and QD655 coated with carboxylic acid werestudied for 8 and 24 h in flow-through diffusion cells with flexed, tapestripped and abraded rat skin to determine if these mechanical actionscould perturb the barrier and affect penetration. Confocal microscopydepicted QD621 penetration through the uppermost layers of the stratumcorneum (SC) and fluorescence was found in the SC and near hairfollicles. QD621 were found in the intercellular lipid layers of the SCby transmission electron microscopy (TEM). QD565 and 655 with flexed andtape-stripped skin did not show penetration; only abraded skin showedpenetration in the viable dermal layers. In all QD studies, inductivelycoupled plasma-optical emission spectroscopy (ICP-OES) analysis forcadmium (Cd) and fluorescence for QD did not detect Cd or fluorescencesignal in the perfusate at any time point, concentration or type of QD.These results indicate that porcine skin penetration of QD621 is minimaland limited primarily to the outer SC layers, while QD565 and 655penetrated into the dermis of abraded skin. The anatomical complexity ofskin and species differences should be taken into consideration whenselecting an animal model to study nanoparticle absorption/penetration.These findings are of importance to risk assessment for nanoscalematerials because it indicates that if skin barrier is altered such asin wounds, scrapes, or dermatitis conditions could affect nanoparticlepenetration deeper into the dermal layers and skin is an important organand can serve as a potential route of exposure and should not beoverlooked.