Sandra Nystrom and Margaret Hart Age/Grade Level: 9th/10th grade Biology and Physics Lesson length: 2 days Topic/Goal is for students to: Gain an understanding about ways that the “unseen” can be “seen” Understand basic principles behind fluorescence Apply knowledge to detect a “tumor” using fluorescent imaging. Apply knowledge of the electromagnetic spectrum to imaging techniques. (In Biology) This lesson would be performed after students learn about mitosis and what happens when mitosis is uncontrolled (a growth). (In Physics) This lesson would be performed after the students have an introduction to electromagnetic spectrum. Students would have been introduced to the reflectance and absorbance of light. Link to National Science Standards: CONTENT STANDARD A: As a result of activities in grades 9-12, all students should develop o Abilities necessary to do scientific inquiry o Understandings about scientific inquiry CONTENT STANDARD E: As a result of activities in grades 9-12, all students should develop o Abilities of technological design o Understandings about science and technology Link to Physics Frameworks (9-10): 6.1 Describe the electromagnetic spectrum in terms of wavelength and energy, and be able to identify specific regions such as visible light. 6.2 Explain how the various wavelengths in the electromagnetic spectrum have many useful applications such as radio, television, microwave appliances, and cellular telephones. 6.4 Recognize and explain the ways in which the direction of visible light can be changed. Essential Question: How can we image things that we cannot “see”? Interest Building/Introduction to lesson motivator: “Letterheads” (sheets attached FOSS sheet); This introduces the concept of mapping a hidden object by looking at cross-sections. Helpful in locating a tumor, cyst, other soft tissue. (MRI) Students use the skill of piecing together information to locate an object—decipher the “unknown”. Hyperspectral Imaging Connection Activity Introduce the idea that an object may be easier or harder to detect when imaged with different wavelengths of visible light. After students decipher one or two other classmates letters, they will be handed color filters. They now will look at two more letterheads, but this time looking through the filters. They will try to recreate the image again. See Worksheet. (this activity can be done with just looking at one letterhead with the different filters and recording the differences in what the students see) Explain the connection between the color filters and the dye used in tumor detection: Using color filters can bring out an object, or characteristics of an object. But sometimes it takes a bit of finesse and manipulation in order to see what you want with certain wavelengths of light. One example of this is used in the detection of tumors in the human body. The body is injected with a certain dye that gets absorbed by the tumors faster and more concentrated than the skin. Then, when blue light shines on the skin and the tumor, the tumor flouresceses, or glows. You can think of the dye as a color filter that allows the right wavelength of light to be reflected back to your eyes so you can see the tumor more easily. How does a glowstick work? Have students come up with answers to this question and make a list on the board. When list is complete, discuss the reaction with them. What other things “glow” in nature? (fireflies, some jellyfish, dinoflagellates) Scientists can locate things in the body by introducing chemicals that bind to other chemicals/cells/structures in the body. When hit with a certain wavelength of light (usually in UV or infrared spectrum), they become “excited”. As the electrons fall to lower energy level, energy is realeased in the form of light. Modeling Skin Cancer Detection and removal with Fluorescence: See Attached Sheet for instructions Materials: 1. uncolored playdough 2. uncolored playdough with tonic water added to it in place of regular water 3. black light Modeling the Imaging of a Skin Tumor using Fluorescent Spectroscopy You are a dermatological surgeon. Your patient has come to you with a suspicious looking mole on his arm. Traditionally, a biopsy would be done on the mole and it would be taken to a lab to be viewed for cancerous cells. This procedure can take from 2-days to 1-week to obtain results. You ask your patient is he would like to take part in a “cutting-edge” clinical trial, which uses tumor- specific chemicals to stain the skin and can be done in a matter of an hour. He asks how it works. You explain that “When hit with appropriate wavelengths of light, the tumor cells fluoresce. This fluorescence is captured by a special camera (CCD), and imaged using a unique computer program. This type of detection allows for rapid analysis of the tissue without any actual cutting.” Your patient agrees and you and a cooperating physician begin the procedure. The protocol to follow is listed below: 1. Apply the fluorescent dye to the area of interest. (This has been done for you ahead of time). 2. In order to obtain depth images, you will use the ceramic wire tool to make slices of the skin model. (Remember that this does not mean you are actually cutting the skin. You are modeling the skin image being taken by the computer). 3. Cut a 1 cm lateral section off of the skin model and place onto the provided layout sheet. 4. Shine the light source onto the model. 5. Use the provided marker to trace any area that is fluorescing. Trace directly onto the skin model. 6. You have just taken your first computer image. 7. Repeat steps 3-6 until you image two sections that do not fluoresce. 3-D Imaging of the Tumor You have detected the tumor’s cross sectional images. Now it is time to create the 3-D image of only the cancerous tissue. Brainstorm with your cooperating physician how you can achieve this. You may have to manipulate the images. This is a critical step in order to precisely remove the cancerous tissue when it comes time for surgery. Write down your idea and show it to the “Head Physician” before creating it. FLUORESCENT IMAGING SHEET Top of skin sample Sketch of cancerous tissue Ideas for 3-D image Bottom of skin sample Assessment 1. Successful creation of a 3-D image of the tumor. 2. Describe two advantages that using light to detect tumors has over the traditional methods of tumor diagnosis (biopsy). 3. What properties must be present in the object/tissue of interest in order for a light imaging system to work? 4. Describe any difficulties you had during this activity. Think of a way to improve the procedure and describe it below. Be creative, there is no right answer! 5. Using this activity as an example, explain why it is important for scientists and engineers across disciplines to work together in research. LUMINESCENCE Taken from www.howstuffworks.com How lightsticks work The chemical reaction in a light stick usually involves several different steps. A typical commercial light stick holds a hydrogen peroxide solution and a solution containing a phenyl oxalate ester and a fluorescent dye. Here's the sequence of events when the two solutions are combined: 1. The hydrogen peroxide oxidizes the phenyl oxalate ester, resulting in a chemical called phenol and an unstable peroxyacid ester. 2. The unstable peroxyacid ester decomposes, resulting in additional phenol and a cyclic peroxy compound. 3. The cyclic peroxy compound decomposes to carbon dioxide. 4. This decomposition releases energy to the dye. 5. The electrons in the dye atoms jump to a higher level, then fall back down, releasing energy in the form of light. When you bend the plastic stick, the glass vial snaps open, and the two solutions flow together. The chemicals immediately react to one another, and the atoms begin emitting light. The particular dye used in the chemical solution gives the light a distinctive color. Depending on which compounds are used, the chemical reaction may go on for a few minutes or for many hours. If you heat the solutions, the extra energy will accelerate the reaction, and the stick will glow brighter, but for a shorter amount of time. If you cool the light stick, the reaction will slow down, and the light will dim. If you want to preserve your light stick for the next day, put it in the freezer -- it won't stop the process, but it will drag out the reaction considerably. Light sticks are just one application of an important natural phenomenon -- luminescence. Generally speaking, luminescence is any emission of light that is not caused by heating. Among other things, luminescence is used in televisions, neon lights and glow-in-the-dark stickers. It's also the principle that lights up a firefly and makes some rocks glow after dark. What Does Luminol Do? Much of crime scene investigation, also called criminalistics, is based on the notion that nothing vanishes without a trace. This is particularly true of violent crime victims. A murderer can dispose of the victim's body and mop up the pools of blood, but without some heavy-duty cleaning chemicals, some evidence will remain. Tiny particles of blood will cling to most surfaces for years and years, without anyone ever knowing they're there. The basic idea of luminol is to reveal these traces with a light-producing chemical reaction between several chemicals and hemoglobin, an oxygen-carrying protein in the blood. The molecules break down and the atoms rearrange to form different molecules (see this site for more information on chemical reactions). In this particular reaction, the reactants (the original molecules) have more energy than the products (the resulting molecules). The molecules get rid of the extra energy in the form of visible light photons. This process, generally known as chemiluminescence, is the same phenomenon that makes fireflies and light sticks glow. Investigators will spray a suspicious area, turn out all the lights and block the windows, and look for a bluish-green light. If there are any blood traces in the area, they will glow. The "central" chemical in this reaction is luminol (C8H7O3N3), a powdery compound made up of nitrogen, hydrogen, oxygen and carbon. Criminalists mix the luminol powder with a liquid containing hydrogen peroxide (H2O2), a hydroxide (OH-) and other chemicals, and pour the liquid into a spray bottle. The hydrogen peroxide and the luminol are actually the principle players in the chemical reaction, but in order to produce a strong glow, they need a catalyst to accelerate the process. The mixture is actually detecting the presence of such a catalyst, in this case the iron in hemoglobin (see this site for more information on catalysts). To perform a luminol test, the criminalists simply spray the mixture wherever they think blood might be. If hemoglobin and the luminol mixture come in contact, the iron in the hemoglobin accelerates a reaction between the hydrogen peroxide and the luminol. In this oxidation reaction, the luminol loses nitrogen and hydrogen atoms and gains oxygen atoms, resulting in a compound called 3- aminophthalate. The reaction leaves the 3-aminophthalate in an energized state -- the electrons in the oxygen atoms are boosted to higher orbitals. The electrons quickly fall back to a lower energy level, emitting the extra energy as a light photon (see this page for more information on light production). With iron accelerating the process, the light is bright enough to see in a dark room. Investigators may use other chemiluminescent chemicals, such as fluorescein, instead of luminol. These chemicals work the same basic way, but the procedure is a little bit different.