In the Classroom edited by
Erica K. Jacobsen Journal of Chemical Education
Classroom Activity Connections: Lessons from Fluorescence Aoife MacCormac,* Emma O'Brien, and Richard O'Kennedy Biomedical Diagnostics Institute, National Centre for Sensor Research, Dublin City University, Glasnevin, Dublin 9, Ireland *
[email protected] Students of all ages enjoy the beautiful and fascinating phenomenon of fluorescence. Fluorescence occurs when an object absorbs electromagnetic radiation at a certain wavelength of the spectrum and re-emits it as radiation at a different, often longer wavelength. One of the more common ways this happens is with UV light (longwave, black light). Many objects absorb UV light and re-emit it as visible light in a variety of colors. The fluorescence of many items has been examined in past JCE Classroom Activities and related articles (1-8). In particular, JCE Classroom Activity #68 “Turning on the Light” (1) describes the science behind fluorescence, phosphorescence, and tribloluminescence and a number of activities to compare these phenomena. To see fluorescence in action in this activity, students examine a number of items under UV light, such as markers, stickers, chlorophyll (isolated from spinach), and rocks containing the mineral fluorite and record their color and intensity. In this Classroom Activity Connections article, we describe some other everyday items that can be examined under UV light and some extensions that can be done in the classroom on fluorescence. Students can look at these items themselves under UV light or the activity can be done as a demonstration by the teacher, depending on resources. After being introduced to the concepts of fluorescence and observing the objects fluorescing, students should be able to understand how fluorescence works and have an appreciation of the fact that many common, everyday items can exhibit fluorescence. Procedure The procedure from JCE Classroom Activity #68 is followed. Each item is examined under longwave UV light and its color and intensity is recorded. A handout combining a list of fluorescent materials from JCE Classroom Activity #68 and this article is provided for the students in the supporting information for this article. Observing Fluorescent Materials Common items whose fluorescence can be observed under UV light are discussed below. Fluorescent Foods and Vitamins Green peppers display a red fluorescence under black light (9) (see Figure 1A). Students can cut the peppers in half and peel off some skin to see how this looks. Other fruits and vegetables that display some fluorescence under UV light are red peppers (blue/green); zucchinis, also known as courgettes (red); tomatoes (blue); lettuce (purple/blue; see Figure 1B); onions (yellow);
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coconuts (when open) (white); and kiwis (red). Bananas also have a bright blue fluorescence under UV light depending on how ripe they are (10) (see Figure 1C). Orange lentils display a strong orange fluorescence under UV light, especially on black paper. Please note the room must be quite dark to see these, but they are quite dramatic, and this demonstration is excellent in emphasizing the fact that fluorescence is everywhere. These foods can display fluorescence because of the presence of chlorophyll. In bananas, the fluorescence is due to chlorophyll breakdown products known as catabolites (10). However, the fluorescence may also be due to other metabolites, or small organic molecules produced by enzymatic reactions in the cells, such as carotenoids and flavonoids. Scientists often use fluorescent markers to carry out certain measurements in plant and animal cells (see Extension 2). However, sometimes these other fluorescent molecules present in cells interfere with these measurements. This is known as autofluorescence and often needs to be considered carefully before certain studies of cells using fluorescence are carried out. Vitamin B-12 tablets exhibit a bright yellow fluorescence under UV light. They can be crushed and added to a dilute acid (such as vinegar) to accentuate this. Nonfood Fluorescent Materials Postage stamps and credit cards (11) also exhibit fluorescence, as do crystals such as calcite and quartz (readily available from rock shops). Some seashells, such as cowry shells also display fluorescence. Students can also have fun looking at the sleeves of their sweaters under UV light, particularly when they are made of dark material: the UV light reveals lint and other details that cannot be seen in ordinary light. Many more fluorescent fruits, vegetables, and other items not reported here do in fact fluoresce, so students could enjoy examining some other items under UV light to see whether they display fluorescence. Extending the Lessons from Fluorescence Extension 1: Light, Color, and Art Students can show their creative side and build a fluorescent art piece under UV light. For example, they can arrange the classic “bowl of fruit” (a wooden bowl works best) and expose to UV light for dramatic effect! Students can try with the foods both whole and cut open. Students can also create fluorescent landscapes, using the items listed above and other items reported to be fluorescent such as tonic water, washing powder, and highlighter ink. For example, they can
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r 2010 American Chemical Society and Division of Chemical Education, Inc. pubs.acs.org/jchemeduc Vol. 87 No. 7 July 2010 10.1021/ed100262t Published on Web 05/05/2010
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In the Classroom
Figure 1. (A) Green pepper (cut open) under UV light; (B) lettuce under UV light; (C) bananas under UV light.
create a snowy landscape with washing powder on black paper, or a desert landscape using orange lentils, perhaps with a “pool” of tonic water (in a Petri dish). Extension 2: Researching Applications of Fluorescence Students can undertake a research project on the applications of fluorescence in medicine. In particular, GFP (Green Fluorescent Protein) is a good topic to spark the student's interest. In 2008, the Nobel Prize in Chemistry was won, in part, for research on GFP (12, 13). This fluorescent protein is found in jellyfish and had been used in a number of important applications in medicine. It glows green when blue light is shone on it. It is a relatively small protein, so the DNA that codes for the protein can be “tagged” onto certain genes (or sequences of DNA that code for a particular protein) within a cell. Researchers can tell if a particular protein is being made or “expressed” in a cell at a particular time by using fluorescence microscopy. This technique involves exposing the specimen to blue light and then measuring the bright green fluorescence exhibited by the GFP tag to indicate the presence of the protein (14, 15). Acknowledgment The authors would like to thank Science Foundation Ireland for funding under Grant No. 06/UR/B921, and the Royal Dublin Society. Literature Cited 1. O'Hara, P.; Engelson, C.; St. Peter, W. Turning on the Light. J. Chem. Educ. 2005, 82, 48A–48B. 2. O'Hara, P.; Engelson, C.; St. Peter, W. Turning on the Light: Lessons from Luminescence. J. Chem. Educ. 2005, 82, 49–52. 3. Muyskens, M. pHantastic Fluorescence. J. Chem. Educ. 2006, 83, 768A–768B.
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4. Muyskens, M. The Fluorescence of Lignum nephriticum: A Flash Back to the Past and a Simple Demonstration of Natural Substance Fluorescence. J. Chem. Educ. 2006, 83, 765–768. 5. Wahab, M. Fluorescent Fun: Using a Homemade Fluorometer. J. Chem. Educ. 2007, 84, 1312A–1312B. 6. Wahab, M. Fluorescence Spectroscopy in a Shoebox. J. Chem. Educ. 2007, 84, 1312. 7. Weinberg, R. B. How Does Your Laundry Glow? J. Chem. Educ. 2007, 84, 800A–800B. 8. Weinberg, R. B. An Iodine Fluorescence Quenching Clock Reaction. J. Chem. Educ. 2007, 84, 797–800. 9. Broderick, C. E.; Cooke, P. Fluorescence Imaging of Habanero and Bell Pepper Fruits. Microsc. Microanal. 2007, 13 (Suppl. 2), 276– 277. 10. Kemsley, J. Yellow Bananas Fluoresce Blue. Chem. Eng. News 2008, 86 (42), 51. 11. New Zealand's Science Learning Hub: You, Me and UV; UV and Fluorescence. http://www.sciencelearn.org.nz/contexts/you_me_and_uv/ science_ideas_and_concepts/uv_and_fluorescence (accessed Apr 2010). 12. Web Site of the Nobel Foundation, Nobel Prize in Chemistry, 2008. http://nobelprize.org/nobel_prizes/chemistry/laureates/2008/ (accessed Apr 2010). 13. Caldwell, B. A. Science Underlying 2008 Nobel Prizes. J. Chem. Educ. 2009, 86, 71. 14. Pieribone, V.; Gruber, D. Aglow in the Dark: The Revolutionary Science of Biofluorescence; Belknap Press: Cambridge, 2006. 15. Zimmer, M. Glowing Genes: A Revolution in Biotechnology; Prometheus Books: Buffalo, NY, 2005.
Supporting Information Available The procedure instructions and a data table ready for students to add their observations are available. This material is available via the Internet at http://pubs.acs.org.
pubs.acs.org/jchemeduc
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r 2010 American Chemical Society and Division of Chemical Education, Inc.
