Penetration of Intact Skin by Quantum Dots with Diverse Physicochemical Properties

TLDR

Skin is the largest organ and a potential route of exposure to engineered nanomaterials, but its permeability to these materials is unknown. The study aimed to determine whether quantum dots could penetrate intact skin in a size‑ or coating‑dependent manner. Commercially available quantum dots of two core/shell sizes/shapes and three surface coatings were topically applied to porcine skin in flow‑through diffusion cells at an occupationally relevant dose for 8 h and 24 h, and penetration was assessed by confocal microscopy. Spherical 4.6 nm QDs penetrated the stratum corneum and reached epidermal and dermal layers by 8 h, while ellipsoid 12 × 6 nm QDs with neutral or cationic coatings localized in the epidermis by 8 h and the carboxylic‑acid coating only after 24 h, demonstrating that quantum dots of diverse physicochemical properties can penetrate intact skin within a typical workday.

Abstract

Skin is the largest organ of the body and is a potential route of exposure to engineered nanomaterials, but the permeability of the skin to these nanomaterials is unknown. We selected commercially available quantum dots (QD) of two core/shell sizes and shapes and three different surface coatings to determine if QD could penetrate intact skin in a size- or coating-dependent manner. Spherical 4.6 nm core/shell diameter QD 565 and ellipsoid 12 nm (major axis) by 6 nm (minor axis) core/shell diameter QD 655 with neutral (polyethylene glycol), anionic (carboxylic acids) or cationic (polyethylene glycol-amine) coatings were topically applied to porcine skin in flow-through diffusion cells at an occupationally relevant dose for 8 h and 24 h. Confocal microscopy revealed that spherical QD 565 of each surface coating penetrated the stratum corneum and localized within the epidermal and dermal layers by 8 h. Similarly, polyethylene glycol– and polyethylene glycol-amine–coated ellipsoid QD 655 localized within the epidermal layers by 8 h. No penetration of carboxylic acid–coated QD 655 was evident until 24 h, at which time localization in the epidermal layers was observed. This study showed that quantum dots of different sizes, shapes, and surface coatings can penetrate intact skin at an occupationally relevant dose within the span of an average-length work day. These results suggest that skin is surprisingly permeable to nanomaterials with diverse physicochemical properties and may serve as a portal of entry for localized, and possibly systemic, exposure of humans to QD and other engineered nanoscale materials.