Photoactivity tests of TiO 2 and ZnO sunscreen ingredients
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Photoactivity tests of TiO2 and ZnO sunscreen ingredients Zuzanna. A. Lewicka1 and Vicki. L. Colvin2* 1
Applied Physics Program, Department of Electrical and Computer Engineering, 6100 Main Street MS-60, Rice University, Houston TX 77005, USA 2
Department of Chemistry, Rice University, Rice University, Houston TX 77005, USA
*Corresponding author: Phone: 713-348-5741, Fax: 713-348-2578, E-mail: [email protected] ABSTRACT Nanosized titanium dioxide (TiO2) and zinc oxide (ZnO) are widely used as inorganic sunscreen pigments. However, these metal oxide particles may also be photocatalytic and generate DNA-damaging reactive oxygen species. Therefore, we evaluated the photochemical properties of the whole sunscreen emulsions that contained nanoscale components and the inorganic particles derived from these sunscreens using several assays such as dichlorofluorescein fluorescence, the decolorization of Congo red dye and DMPO spin trap electron paramagnetic resonant spectroscopy. The results of these three tests showed that samples with ZnO nanoscale materials were more photoactive than the samples that contained TiO2 nanoparticles. INTRODUCTION The retail suncare product sector has been an area of rapid growth during the past decade, with a market size in excess of one billion dollars in the US alone [1]. This growth is driven by consumers who use suncare products to prevent skin cancer and minimize premature aging [2]. Moreover, ultraviolet protection is now a standard feature in everyday items such as moisturizers and cosmetics [3]. These products use ultraviolet blocking agents, either organic molecules or inorganic pigments, to absorb damaging radiation before it can interact with skin. The sun protection that results from using nanosized titanium dioxide and zinc oxide particles is more effective than that found in formulations with larger particles [4]. Consumers may also prefer suncare products made with nanoparticles as they have a smooth feeling and transparent appearance. However, non-governmental organizations and even some governments have noted the potential risks associated with nanosized ultraviolet blocking agents [5-7]. Because both ZnO and TiO2 can catalytically produce reactive oxygen species (ROS) upon ultraviolet illumination, the possible hazard of these materials has received intensive study in the toxicology community [8-10]. In contact with cells, TiO2 and ZnO nanoparticles that are synthesized in research laboratories or obtained from chemical companies react with these biological molecules and lead to their oxidative damage. Research has also shown that inorganic materials extracted from commercial sunscreens had potency in generating free radicals in cell free assays and in vitro tests [11-15]. Here, in this study we investigate whether commercially available sunscreens that contain nanoscale TiO2 and ZnO particles generate ROS species by using a few cell free assays. This project is a part of the work that the goal is to provide sufficient characterization of nanoscale
inorganic materials use
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