THE SCIENCE BEHIND NANOSUN-SCREENS: LEARNING ABOUT NANOPARTICULATE INGREDIENTS USED TO BLOCK THE SUN’S ULTRAVIOLET RAYS.

“What are ‘nano’ ingredients, and how can you tell if your sunscreen has them?” “Why do we need nanosunscreens?” “If a bottle of a well-known sunscreen brand claims that it protects against UVB and UVA rays, should I believe it?” These are just a few of the questions that our “Clear Sunscreen” nanoscience unit has students asking. Students are excited to learn about science that is applicable to their daily lives and because they find the topic interesting, they are motivated to figure out the complex concepts involved. In this article, we provide a brief overview of the emerging field of nanoscience and why it is an important area for education. We then explain the science behind the new nanoparticulate sunscreens, describe the different elements of the unit, and reflect on some of the opportunities and challenges of teaching nanoscience at the high school level. Clear Sunscreen Clear Sunscreen is one of four sets of learning materials collaboratively created by educational researchers, science teachers, and nanoscientists as part of the NanoSense project, aimed at helping high school students learn about science concepts that account for nanoscale phenomena. All of the materials are freely available online and are linked to the National Science Education Standards (NRC 1996) (see “On the web” at the end of this article), as well as related chemistry, physics, biology, and environmental science concepts. Although Clear Sunscreen was designed for chemistry classrooms–introductory, Advanced Placement, or International Baccalaureate, depending on whether the advanced materials are used–it has also been used successfully in 9th-grade biology and 11th-grade biotechnology classrooms. Given the interdisciplinary nature of the content, it could also be used in physics or integrated science classrooms. Throughout the unit, students explore answers to the questions posed in the introduction through presentations, discussions, readings, hands-on activities, and labs. At its conclusion, students synthesize their learning by creating consumer awareness pamphlets that explain the basics of nanoparticulate zinc oxide: how it can appear clear in sunscreens, but still protect against ultraviolet (UV) light; what its benefits are over traditional ingredients; and any potential dangers that might be associated with its use. About nanoscience Nanoscience is the study of matter on the scale of 1-100 nanometers (nm) in at least one dimension. Given that 10 hydrogen atoms lined up are about 1 nm long, we can loosely describe the field as being concerned with molecules and small clusters of molecules in this size range. One well-known example is Buckminsterfullerene, the soccer ball–shaped carbon ([C.sub.60]) molecule often referred to as a “buckyball.” Nanoscience is an important emerging area of research because matter at this size scale has many unique properties. For example, nanosized carbon tubes are 100 times stronger than bulk steel but are also incredibly flexible, and nanosized substances’ melting points decrease as they get smaller. Nanosized zinc oxide–a common ingredient in nanosunscreens–in particular, appears clear (transparent) instead of white. While research is ongoing, the unique properties of nanosized materials have already enabled new innovations in areas as diverse as textiles (e.g., stain-resistant clothes), the environment (e.g., paint that “cleans” the air), and personal health care (e.g., clear nanoparticulate sunscreen). Despite their potential benefits, objects at this size scale still present many mysteries. For instance, they are small enough that many of our models for bulk substances do not accurately predict their properties, but large enough that quantum calculations are prohibitively complicated. Currently, new models and ways of thinking are being developed to better understand their behavior. Introducing nanoscience ideas to students presents several exciting opportunities.