Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM...
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Transcript of Copyright © 2005 SRI International Nano Sunscreen Adapted from the NanoSense web materials STEM...
Copyright © 2005 SRI International
Nano Sunscreen
Adapted from the NanoSense web materials
STEM ED/CHM Nanotechnology 2007
2
Nano Products
• Number of products using nanomaterials is growing very rapidly– Doubling every year?
• Clothing, food and beverages, sporting goods, coatings, cosmetics, personal care
• Sunscreens: today many (most?) use nanomaterials– Some labeled as containing nanoparticles– Some not labeled
3
Why Use Sunscreen?
Too much unprotected sun exposure leads to:
• Premature skin aging (e.g. wrinkles)
• Sunburns
• Skin cancer
Sources: http://www.oasishospital.org/previousnews.html; http://wohba.com/archive/2005_03_01_archive.html
4
Skin Cancer Rates are Rising Fast
Skin cancer:• ~50% of all cancer
cases• > 1 million cases
each year (US)• Causes 1 person to
die every hour (US)
Probability of getting skin cancer:1930 : 1 in 5,0002004 : 1 in 652050 : 1 in 10…
http://www.skincarephysicians.com/skincancernet/whatis.html; http://www.msu.edu/~aslocum/sun/skincancer.htm
Causes of the increase:• Decrease ozone protection• Increased time in the sun• Increased use of tanning beds
Sources: http://www.msnbc.msn.com/id/8379291/site/newsweek/ ;
wavelength
Frequency = number of waves per second
Wavelength = distance from one wave peak to the next
Frequency x wavelength = speed of light
About Light Waves
Higher frequency shorter wavelength
6
The Sun’s Radiation Spectrum
• ~ 43% is in the visible range
• ~ 49% is in the near infrared range
• ~ 7% is in the ultraviolet range
• < 1% is x-rays, gamma waves, and radio waves
.
Most of the sun’s radiation is Ultraviolet (UV), Visible & Infrared (IR) :
Source: Adapted from http://www.ucar.edu/learn/imgcat.htm
7
Energy Comes in Packets or Photons
• The energy of a photon (E) is determined by the frequency of the radiation (f)
E = h x fE fE
f
• Radiation with a higher frequency has more energy in each photon
• The amount of energy in a photon determines how it interacts with our skin
• The total light energy is determined by the number of photons
8
Skin Damage
• The kind of skin damage is determined by the size of the photon ( E = h x f)
• The UV spectrum is broken into three parts: – Very High Energy (UVC)– High Energy (UVB) – Low Energy (UVA)
High Energy Low Energy
Source: http://www.arpansa.gov.au/is_sunys.htm
• As far as we know, visible and IR radiation don’t harm the skin
9
• Very high energy radiation (UVC) is currently blocked by the ozone layer (ozone hole issue)
• High energy radiation (UVB) does the most immediate damage (sunburns)
• But lower energy radiation (UVA) can penetrate deeper into the skin, leading to long term damage
Source: N.A. Shaath. The Chemistry of Sunscreens. In: Lowe NJ, Shaath NA, Pathak MA, editors. Sunscreens, development, evaluation, and regulatory aspects. New York: Marcel Dekker; 1997. p. 263-283.
Skin Damage II
10
So many sunscreens ….
New and Improved
Now with Nano-Z
SPF 50Goes on Clear
Safe for Children
Broadband Protection
11
Sources: http://www.shop.beautysurg.com/ProductImages/skincare/14521.jpg and http://www.shop.beautysurg.com/ProductImages/skincare/14520.jpg
The SPF Rating
• SPF (Sunscreen Protection Factor) Number– Measures the strength of
UVB protection only– Doesn’t tell you anything
about protection from UVA– Most (all?) now claim
UVA/B protection
• Sunscreens first developed to prevent sunburn– Ingredients were good UVB blockers
12
The UVA Problem
• UVA rays have no immediate visible effects but cause serious long term damage – Cancer– Skin aging
• Sunscreen makers working to find UVA blockers– No official rating of UVA
protection yetSource: http://www.cs.wright.edu/~agoshtas/fig8.jpg
Twenty different skin cancer lesions
13
Sunscreen Ingredients
• Lotion • Several active
ingredients in colloidal suspension–Organic– Inorganic
14
Organic Ingredients: The Basics
• Organic = Carbon Atoms– Hydrogen, oxygen & nitrogen
atoms are also often involved• Structure
– Covalent bonds– Exist as individual molecules
• Size – Molecular formula determines
size– Typically a few to several dozen
Å (<10 nm)
Sources: http://www.3dchem.com/molecules.asp?ID=135# and original image
Octyl methoxycinnamate (C18H26O3)
an organic sunscreen ingredient
15
Organic Ingredients: UV Absorption
1. Electrons capture the energy from UV rays
2. They jump to higher energy levels
3. The energy is released as infrared rays which are harmless (each ray is low in energy)
Source: Adapted from http://www.3dchem.com/molecules.asp?ID=135#and http://members.aol.com/WSRNet/tut/absorbu.htm
hf=2.48 eV 3hf=2.48 eV
16
Organic Ingredients: Absorption Range
• Organic molecules only absorb UV rays whose energy matches difference between electron energy levels – Different kinds of molecules have different
peaks and ranges of absorption– Using more than one kind of ingredient
(molecule) gives broader protection
One Ingredient Two Ingredients Three Ingredients
Source: Graphs adapted from http://www.aims.gov.au/pages/research/projects/sunscreens/pages/sunscreens02.html
17
Organic Ingredients: Absorption Range cont.
• Most organic ingredients that are currently used were selected because they are good UVB absorbers– The FDA has approved 15 organic ingredients
• Sunscreen makers are trying to develop organic ingredients that are good UVA blockers– Avobenzone (also known as Parasol 1789) is a
new FDA approved UVA blocker
Source: http://jchemed.chem.wisc.edu/JCEWWW/Features/MonthlyMolecules/2004/Oct/JCE2004p1491fig4.gif
18
How are inorganic sunscreen ingredients different from organic
ones?
19
Inorganic Ingredients: The Basics
• Atoms Involved– Zinc or Titanium– Oxygen
• Structure– Ionic attraction– Cluster of ions– Formula unit doesn’t dictate
size• Size
– Varies with # of ions in cluster– ~10 nm – 300 nm
Source: http://www.microspheres-nanospheres.com/Images/Titania/TIO2%20P7.jpg and image adapted from http://www.cse.clrc.ac.uk/msi/projects/ropa.shtml
Group of TiO2 particles
Detail of the ions in one cluster
20
Inorganic Ingredients: Cluster Size
• Inorganic ingredients come in different cluster sizes (sometimes called “particles”)– Different number of ions can cluster together– Must be a multiple of the formula unit
• ZnO always has equal numbers of Zn and O atoms
• TiO2 always has twice as many O as Ti atoms
~100 nm TiO2 particle ~200 nm TiO2 particle
Source: Images adapted from http://www.cse.clrc.ac.uk/msi/projects/ropa.shtml
21
Inorganic Ingredients: UV Absorption
• Inorganics have a different absorption mechanism than organics
• Absorb consistently through whole UV range up to ~380nm
Source: Graph adapted from http://www.aims.gov.au/pages/research/projects/sunscreens/pages/sunscreens02.html
22
Inorganics: Appearance Matters
• Traditional inorganic sunscreens appear white on our skin (not cool!)
• Many people don’t like how this looks, so they don’t use sunscreen with inorganic ingredients
• Of the people who do use them, most apply too little to get full protection
Source: http://www.4girls.gov/body/sunscreen.jpg
23
Why Do They Appear White?
• Traditional ZnO and TiO2
clusters are large– (> 200nm)
• Large clusters scatter visible light – (400-700 nm) – Maximum scattering occurs
for wavelengths twice as large as the clusters
• The scattered light is reflected to our eyes, appearing white
Source: Original image
24
Waves and obstacles
• Waves go around small obstacles
• Waves scatter all around from obstacles of sizes comparable to a wavelength– Ocean waves scatter
off big rocks, go around small ones
• Nano size particles (< 100 nm) will not scatter visible light and nano sunscreen appears clear
Nanosized ZnO particles
Large ZnO particles
25
Questions to investigate
1. Does the opacity of a substance (to visible light) relate to its ability to block UV light?
2. Does a particular sunscreen block UV A?
3. How do you know if a sunscreen has “nano” ingredients?
26
UV experiments
• 2 setups at each table
• UV sensitive testers (flattened beads) sensitive to 360 – 300 nm light
• UV A lamps• Share some test
materials (see list in handout)
27
UV Detecting Beads
• Absorb 360 – 300 nm light• Includes high energy end of UV A (400 –
320 nm) and low energy part of UV B (320 -280 nm)
Source: http://www.arpansa.gov.au/is_sunys.htm
UV detecting bead wavelengths
28
Farewell gift – UV sensitive kit
• ~25 beads, assorted colors
• ~ 1 yard of rawhide
• Make a necklace or bracelet (s)