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Lesson: Explore the Nano in Sunblock

sunblock(Lesson courtesy NISE Net.org, as part of its NanoDays 2011 activities). Level: K-12. Time Required: 15 to 20 minutes. Lesson Pdfs in English and Spanish.

Overview

Sunblocks containing nanoparticles are one of the most common applications of nanotechnology. In this quick, hands-on lesson using everyday materials, students in grades K-12 compare sunblock containing nanoparticles to those that do not and learn how nanoparticles are used to help block harmful rays from the sun.

Learning Objectives

Students will learn that:

  • Sunblocks containing nanoparticles are one of the most common applications of nanotechnology
  • Nanoparticles in sunblock are invisible to the human eye because they’re smaller than the wavelength of visible light.

Standards

Science and Technology: K-12

  • Abilities of technological design

Science in Personal and Social Perspectives:

  • K-4: Personal health
  • 5-8: Risks and benefits
  • 9-12: Personal and community health

Vocabulary

Nano is the scientific term meaning one-billionth.  (1/1,000,000,000)  It comes from a Greek word meaning “dwarf.”

A nanometer is one one-billionth of a meter. One inch equals 25.4 million nanometers. A sheet of paper is about 100,000 nanometers thick. A human hair measures roughly 50,000 to 100,000 nanometers across. Your fingernails grow one nanometer every second. (Other units can also be divided by one billion. A single blink of an eye is about one-billionth of a year. An eyeblink is to a year what a nanometer is to a yardstick.)

Nanoscale refers to measurements of 1 – 100 nanometers.  A virus is about 70 nm long. A cell membrane is about 9 nm thick. Ten hydrogen atoms are about 1 nm. At the nanoscale, many common materials exhibit unusual properties, such as remarkably lower resistance to electricity, or faster chemical reactions.

Nanotechnology is the manipulation of material at the nanoscale to take advantage of these properties. This often means working with individual molecules.

Nanoscience, nanoengineering and other such terms refer to those activities applied to the nanoscale. “Nano,” by itself, is often used as short-hand to refer to any or all of these activities.

Materials

For each pair of students:

  • A dab of sunblock with nanoparticles of zinc oxide (e.g. CVS Sunblock with Zinc Oxide Spf 45+)
  • A dab of zinc oxide ointment, a non-nano sunblock (e.g. CVS Zinc Oxide Ointment)
  • 2 squares of black construction paper
  • 2 cotton swabs
  • Particle Size handout

Background

Sunblocks containing nanoparticles are one of the most common applications of nanotechnology. Nanotechnology takes advantage of special properties at the nanoscale. For example, the nanoparticles in sunblock are invisible to the human eye because they’re smaller than the wavelength of visible light.

How can you tell if you sun protection product contains nanoparticles? Check the ingredient list on the product. Ingredients such as avobenzone, oxybenzone, or PABA are chemical sunscreens that do not contain nanoparticles. If the product includes zinc oxide or titanium dioxide, it is a mineral sunblock that probably contains nanoparticles if it is also labeled as “goes on clear” or “invisible.”

(From the related NISE Net lesson, “Invisible Sunblock“:)

Although the public and manufacturers often use the words ”sunblock” and “sunscreen” interchangeably, they technically refer to two different types of sun protectants. Sunblocks refer to sun protectants that contain minerals such as zinc oxide or titanium dioxide. They block about 99% of UV radiation, but non-nano formulations are opaque in nature and users rarely apply the amount recommended for effective protection as a result. Sunscreens refer to chemically based sun protectants, few of which individually protect against both UV-A (320–400 nm) and UV-B (290–320 nm) radiation and are usually combined into broad-spectrum products. Although chemical sunscreens also degrade when exposed to UV light, they are more transparent than traditional mineral sunblocks when rubbed on the skin. In light of this, chemical sunscreens tend to be more popular than mineral sun blocks, even though mineral sun blocks are better at blocking UV radiation and are better for the skin because they do not degrade.

When the diameter of a zinc oxide molecule is reduced below the wavelength of visible light (380–780 nm), the nanoparticle no longer scatters visible light so the substance containing the mineral will look transparent. However, the particles are still larger than the wavelength of ultraviolet light and the chemical composition of the particle is not altered, so zinc oxide does not lose its ability to absorb UV radiation.

Nano-safety concerns:
Some people worry that the particle size of the ingredients may make a difference in how safe they are. That’s because materials can act differently when they’re nanosized — so just because something is safe on the microscale doesn’t necessarily mean it’s safe on the nanoscale. More research is needed before we can know for sure.

Nanoparticles used in sun blocks are some of the most extensively researched topics in nanotechnology. Although Australian and European governments have approved the use of nanoparticles in sunblocks, cosmetics are not regulated by the U.S. Food and Drug Administration (FDA). It is often difficult to tell which commercially available products contain nano and non-nano mineral formulations, since cosmetics companies are not required to indicate whether nanoparticles are present in their product.

To date, toxicity studies have shown that nano-zinc and titanium based minerals do not penetrate the outer later of healthy skin and are largely safe to use. However, a possible penetration risk remains in areas where skin is thinner (i.e. lips, underarms, eyelids and at the joints) or if skin has been damaged by prior sun exposure or other physical trauma. Additionally, the elderly and young children may have a higher risk of skin penetration, as these age groups tend to have thinner skin. The primary health concern about nanoparticles is that if they are exposed to UV radiation they can generate oxygen free radicals; these can cause oxidative stress and inflammation as well as damage proteins, lipids and DNA.

Procedure

SAFETY: To avoid potential reactions due to allergies or sensitivities, caution students against applying the ointment or sunblock to their skin.

1. Begin by asking students if they use sunblock. Discuss the purpose of sunblocks/sunscreens in protecting the skin from ultraviolet light, which can cause
 short-term (sunburn) and long-term (pre-mature aging and skin cancer) damage. Expand the discussion to nanotechnology and the use of nano-materials in consumer products. Explain that in this activity, they will be comparing two similar sunblocks, one that employs nano-materials, and another that does not. How does the students imagine they might differ?

2. Divide the class into pairs of two, and distribute to each two black squares of paper and two cotton swabs. Next, distribute small dabs of the ointment and sunblock onto the squares, reminding students to keep in mind which material is which. Explain that both materials  contain zinc oxide, a mineral that is very effective at
 absorbing UV radiation to prevent it from reaching your skin. Before students work the materials, have them predict which one will more easily rub into the paper and become fully translucent.

3. Have the students attempt to rub each dab of sunblock, nano- and non-nano-, into the paper until it disappears. Once they have
 completed the task, ask them to identify which dot disappeared more quickly. What were their observations as they worked with the two materials? What would account for the different outcomes?

Explanation: The difference
 between the two sunblocks is in the size of the zinc oxide particles. The sunblock rubs in better than the ointment, because it contains tiny, nanosized particles of zinc oxide. (A nanometer is a billionth of a meter.) The regular zinc
 oxide leaves a more visible film (a.k.a. “the lifeguard nose”) because the particles
 are large enough to reflect visible light. The nanoparticles of zinc oxide are so small that they don’t reflect visible light, making the sunblock transparent on skin. They are still large
 enough to absorb UV radiation, so protection is equally effective. Both products are equally effective at absorbing UV radiation and keeping it from reaching your skin, but many people prefer sunblock that rubs in clear.

4. Show the students the two pictures of large and small white dots. Ask which 
dots are easier to see; they will likely choose the picture with the large dots. This 
image represents the regular sunblock – the large white dots reflect more visible light 
than the smaller dots, so they are more visible. The image of the small dots
 represents the nano-sunblock – each smaller particle reflects less visible light, so 
collectively they are harder to see and the nano-sunblock appears transparent. The
 large dot image has been scaled down and tiled to form the image of the small
 dots, so the ratio of black to white is the same in both pictures; only the distribution is
 different.

How can you tell if your sun protection product contains nanoparticles? Check the ingredient list on the product. Ingredients such as avobenzone, oxybenzone, or PABA are chemical sunscreens that do not contain nanoparticles. If the product includes zinc oxide or titanium dioxide, it is a mineral sunblock that probably contains nanoparticles if it is also labeled as “goes on clear” or “invisible.”It is a mineral sunblock that works by absorbing UV rays.

Extension

  • Solicit students’ ideas as to why people speak about the potential dangers of nano-scaled materials, then discuss with them current debates and concerns.

  • Have students read ASEE’s Prism magazine November 2010 feature, “Peril in Small Places,” to learn more about research into potential hazards of nano materials.
  • Have students research further into uses of nano materials.

Resources

  • Peril in Small Places,” ASEE’s Prism magazine November 2010 feature exploring the potential hazards of nano materials.

  • NISE Net, The Nanoscale Informal Science Education Network, which creates activities and materials for the annual NanoDays, supports a web page with tools for K-12 teachers, featuring links to introductory materials, downloadable activity packages,  professional development, college-level lectures and curriculum, and publications.
Credits: Developed for NISE Network with funding from the National Science Foundation.

One Response to “Lesson: Explore the Nano in Sunblock”

  1. Corrected the links. Should work now.

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