Saturday, August 02, 2008

Study shows quantum dots can penetrate skin through minor abrasions

pyramid-shaped quantum dots

Caption: Micrograph of pyramid-shaped quantum dots grown from indium, gallium, and arsenic. Each dot is about 20 nanometers wide and 8 nanometers in height.
Researchers at North Carolina State University have found that quantum dot nanoparticles can penetrate the skin if there is an abrasion, providing insight into potential workplace concerns for healthcare workers or individuals involved in the manufacturing of quantum dots or doing research on potential biomedical applications of the tiny nanoparticles.
While the study shows that quantum dots of different sizes, shapes and surface coatings do not penetrate rat skin unless there is an abrasion, it shows that even minor cuts or scratches could potentially allow these nanoparticles to penetrate deep into the viable dermal layer - or living part of the skin - and potentially reach the bloodstream.

Dr. Nancy Monteiro-Riviere, professor of investigative dermatology and toxicology at NC State's College of Veterinary Medicine, tested the ability of the quantum dots to penetrate rat skin at 8 and 24 hour intervals. The experiment evaluated rat skin in various stages of distress - including healthy skin, skin that had been stripped using adhesive tape and skin that had been abraded by a rough surface. The researchers also assessed whether flexing the skin affected the quantum dots' ability to penetrate into the dermal layer. Monteiro-Riviere co-authored the study with doctoral student Leshuai Zhang.

While the study indicates that acute - or short-term - dermal exposure to quantum dots does not pose a risk of penetration (unless there is an abrasion), Monteiro-Riviere notes "there is still uncertainty on long-term exposure." Monteiro-Riviere explains that the nanoparticles may be able to penetrate skin if there is prolonged, repeated exposure, but so far no studies have been conducted to date to examine that possibility. Quantum dots are fluorescent nanoparticles that may be used to improve biomedical imaging, drug delivery and diagnostic testing.

This finding is of importance to risk assessment for nanoscale materials because it indicates that skin barrier alterations - such as wounds, scrapes, or dermatitis conditions - could affect nanoparticle penetration and that skin is a potential route of exposure and should not be overlooked.

The study found that the quantum dots did not penetrate even after flexing the skin, and that the nanoparticles only penetrated deep into the dermal layer when the skin was abraded. Although quantum dots are incredibly small, they are significantly larger than the fullerenes - or buckyballs - that Monteiro-Riviere showed in a 2007 study in Nano Letters can deeply and rapidly penetrate healthy skin when there is repetitive flexing of the skin.

Additionally, Monteiro-Riviere's laboratory previously showed quantum dots of different size, shape and surface coatings could penetrate into pig skin. The anatomical complexity of skin and species differences should be taken into consideration when selecting an animal model to study nanoparticle absorption/penetration. Human skin studies are also being conducted, but "it is important to investigate species differences and to determine an appropriate animal model to study nanoparticle penetration," Monteiro-Riviere says. "Not everyone can obtain fresh human skin for research."

Nanoparticles are generally defined as being smaller than 100 nanometers (thousands of times thinner than a human hair), and are expected to have widespread uses in medicine, consumer products and industrial processes. ###

The study, "Assessment of Quantum Dot Penetration into Intact, Tape-Stripped, Abraded and Flexed Rat Skin," was published in the June issue of Skin Pharmacology and Physiology.

Note to Editors: The study abstract follows.

"Assessment of Quantum Dot Penetration into Intact, Tape-Stripped, Abraded and Flexed Rat Skin"

Authors: L.W. Zhang and N.A. Monteiro-Riviere, North Carolina State University
Published: May 2008, in Skin Pharmacology and Physiology.

Abstract: Quantum dot (QD) nanoparticles have received attention due to their fluorescent characteristics and potential use in medical applications. Skin penetration is one of the major routes of exposure for nanoparticles to gain access to a biological system. QD655 and QD565 coated with carboxylic acid were studied for 8 and 24 h in flow-through diffusion cells with flexed, tape-stripped and abraded rat skin to determine if these mechanical actions could perturb the barrier and affect penetration.

Nonflexed skin did not show QD penetration 8 or 24 h. Flexed skin showed an increase in QD on the surface of the skin but no penetration at 8 and 24 h. Tape-stripped skin depicted QD only on the surface of the viable epidermis. QD655 penetrated into the viable dermal layers of abraded skin at both 8 and 24 h, while QD565 was present only at 24 h. QD were not detected in the perfusate by fluorescence and inductively coupled plasma-optical emission spectroscopy analysis for cadmium at any time point.

These results indicate that the rat skin penetration of QD655 and QD565 is primarily limited to the uppermost stratum corneum layers of intact skin. Barrier perturbation by tape stripping did not cause penetration, but abrasion allowed QD to penetrate deeper into the dermal layers.

Contact: Matt Shipman 919-515-6386 North Carolina State University

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