Whether Quantum Dots are able to penetrate through the skin largely depends on two parameters: (1) the condition of the skin (injured or intact) and (2) the physico-chemical properties of the Quantum Dots themselves.

 

The penetration of Quantum Dots through intact skin was analysed in a porcine skin ex vivo perfusion model [1,2]. In this experimental set-up, the porcine skin was perfused with blood containing different concentrations of Quantum Dots. Depending on the surface modification (either carboxyl (COOH) or PEG) of the Quantum Dots, a larger or lesser amount could be found in skin capillaries, respectively, indicating that uptake could occur from the blood to the skin tissue itself [3]. This confirms earlier work from the same group showing in vitro that COOH-coated Quantum Dots are taken up in greater quantities into human keratinocytes (skin cells) than PEG-coated ones [3].

The same ex vivo model as well as skin cells (keratinocytes, in vitro) were used to assess effects of topically applied Quantum Dots [2]. PEG-coated Quantum Dots were found to only penetrate the uppermost stratum corneum (horned layer of the skin) which consists of dead cells. However the viability of living skin cells (keratinocytes) in vitro decreased with increasing concentrations of the same QDs [2,4].

 

The effects of Quantum Dots on sun-injured skin were assessed using UV-irradiated mouse skin in an in vivo model [5]. It could be shown that after UV exposure a greater amount of Quantum Dots was found in deeper layers of the skin compared to uninjured skin were almost no penetration took place. The authors conclude that amount and depth of Quantum Dots penetration largely depends on the condition of the skin and the characteristics of the Quantum Dots (like e.g. size and surface chemistry) [5].

Furthermore, comparing different skin injury types (“tape stripping, which removes the horned layer only; acetone treatment, dermabrasion, flexing) in mouse and rat models revealed that only dermabraded skin was leaky for Quantum Dots [4,6,7]. Particles were applied to the skin of injured animals as well as uninjured control animals. Approximately 2 % of the applied dose of cadmium (resulting from the Quantum Dots' Cadmium-Selenide cores) could be detected in both the lymph and the liver of dermabraded mice. These results suggest that if skin is reasonably damaged it is possible for Quantum Dots to penetrate into deep layers of the skin and even distribute around the body via the bloodstream [4,7] – at least in this particular mouse model and for this type of Quantum Dots.

 

In summary, it can be concluded from these data that only a very small proportion of superficially administered quantum dots can penetrate the intact skin. However, if the skin is damaged and thus facilitates the penetration of the quantum dots, it may be possible that the application of Quantum Dots may impact or impair the cells of deeper skin layers and trigger inflammatory reactions.

 

 

Literature arrow down

  1. Lee, HA et al. (2007), Nano Lett, 7(9): 2865-2870.
  2. Zhang, LW et al. (2008), Toxicol Appl Pharmacol, 228(2): 200-211.
  3. Ryman-Rasmussen, JP et al. (2007), Nano Lett, 7(5): 1344-1348.
  4. Bottrill, M et al. (2011), Chem Commun (Camb), 47(25): 7039-7050.
  5. Mortensen, LJ et al. (2008), Nano Lett, 8(9): 2779-2787.
  6. Zhang, LW et al. (2008), Skin Pharmacol Physiol, 21(3): 166-180.
  7. Gopee, NV et al. (2009), Toxicol Sci, 111(1): 37-48.

 

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