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Scientists use laser imaging to assess safety of zinc oxide nanoparticles in sunscreen

Date:
December 2, 2011
Source:
Optical Society of America
Summary:
Ultra-tiny zinc oxide (ZnO) particles are among the ingredients list of some commercially available sunscreen products, raising concerns about whether the particles may be absorbed beneath the outer layer of skin. To help answer these questions, a team of scientists from Australia and Switzerland have developed a way to optically test the concentration of ZnO nanoparticles at different skin depths.
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Overlay of the confocal/multiphoton image of the excised human skin. Yellow color represents skin autofluorescence excited by 405 nm; Purple color represents zinc oxide nanoparticle distribution in skin (stratum corneum) excited by 770 nm, with collagen-induced faint SHG signals in the dermal layer.
Credit: Biomedical Optics Express.

Ultra-tiny zinc oxide (ZnO) particles with dimensions less than one-ten-millionth of a meter are among the ingredients list of some commercially available sunscreen products, raising concerns about whether the particles may be absorbed beneath the outer layer of skin. To help answer these safety questions, an international team of scientists from Australia and Switzerland have developed a way to optically test the concentration of ZnO nanoparticles at different skin depths. They found that the nanoparticles did not penetrate beneath the outermost layer of cells when applied to patches of excised skin.

The results, which were published this month in the Optical Society's (OSA) open-access journal Biomedical Optics Express, lay the groundwork for future studies in live patients.

The high optical absorption of ZnO nanoparticles in the UVA and UVB range, along with their transparency in the visible spectrum when mixed into lotions, makes them appealing candidates for inclusion in sunscreen cosmetics. However, the particles have been shown to be toxic to certain types of cells within the body, making it important to study the nanoparticles' fate after being applied to the skin. By characterizing the optical properties of ZnO nanoparticles, the Australian and Swiss research team found a way to quantitatively assess how far the nanoparticles might migrate into skin.

The team used a technique called nonlinear optical microscopy, which illuminates the sample with short pulses of laser light and measures a return signal. Initial results show that ZnO nanoparticles from a formulation that had been rubbed into skin patches for 5 minutes, incubated at body temperature for 8 hours, and then washed off, did not penetrate beneath the stratum corneum, or topmost layer of the skin. The new optical characterization should be a useful tool for future non-invasive in vivo studies, the researchers write.


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The above post is reprinted from materials provided by Optical Society of America. Note: Materials may be edited for content and length.


Journal Reference:

  1. Zhen Song, Timothy A. Kelf, Washington H. Sanchez, Michael S. Roberts, Jaro Rička, Martin Frenz, Andrei V. Zvyagin. Characterization of optical properties of ZnO nanoparticles for quantitative imaging of transdermal transport. Biomedical Optics Express, 2011; 2 (12): 3321 DOI: 10.1364/BOE.2.003321

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Optical Society of America. "Scientists use laser imaging to assess safety of zinc oxide nanoparticles in sunscreen." ScienceDaily. ScienceDaily, 2 December 2011. <www.sciencedaily.com/releases/2011/11/111130115812.htm>.
Optical Society of America. (2011, December 2). Scientists use laser imaging to assess safety of zinc oxide nanoparticles in sunscreen. ScienceDaily. Retrieved July 30, 2015 from www.sciencedaily.com/releases/2011/11/111130115812.htm
Optical Society of America. "Scientists use laser imaging to assess safety of zinc oxide nanoparticles in sunscreen." ScienceDaily. www.sciencedaily.com/releases/2011/11/111130115812.htm (accessed July 30, 2015).

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