Why chemiluminescence is used

When energy in the form of light is released from matter because of a chemical reaction the process is called chemiluminescence. One example of a common chemiluminescent reaction is a flame, where the reaction between a fuel and an oxidant produce excited state products that emit light; however, as an example of chemiluminescence this process is complicated by the fact that incandescent particles are often also present because of the amount of heat released by the reaction; therefore, some or most?

A better example of a chemiluminescent reaction is between nitrogen monoxide symbol NO and ozone O 3. Nitrogen monoxide reacts with ozone to produce nitrogen dioxide NO 2 in an excited state denoted by the raised asterisk. This reaction is catalyzed by the iron located in hemoglobin. It is used at crime scenes to illuminate blood. Luminol can also react with nitric oxide in air to produce an excited aminophthalate anion intermediate that relaxes to produce water, molecular nitrogen, and light.

This reaction is used to detect nitric oxide levels in air to determine pollution levels. Another chemiluminescence example is the reaction of a peroxyoxalate such as bis 2,4,6-trichlorophenyl oxlate TCPO and hydrogen peroxide to produce a high-energy intermediate 1,2-dioxetanedione. A fluorophore such as 9,diphenylanthracene present in the solution will be excited by transfer of the excited electron from the intermediate molecule and will emit light.

Two commonly used enzymes for chemiluminescence reactions are alkaline phosphatase AP and horseradish peroxidase HRP. These enzymes catalyze oxidation of substrates in the presence of hydrogen peroxide oxidizing agent. Whether the reaction produces a simple color change or light is entirely dependent on the choice of substrate. Another fun example of chemiluminescence can be observed in glow sticks.

When the stick is cracked it allows the reaction of the substrate cyalume plus a dye with hydrogen peroxide to proceed to produce an excited dye that emits light. The reaction has a limited lifetime , and the glow stick will eventually lose its luminescence , but it lasts longer than most chemiluminescence reactions.

The dye releases light energy at a slower rate than most high-energy intermediates. This idea can be transferred to the laboratory to extend the lifetime of chemiluminescent reactions and to increase the time available for imaging. In a chemiluminescent magnetic immunoassay CLIA antibodies are labeled with a chemiluminescent substrate.

The corresponding antigen is bound to paramagnetic beads. During an incubation period, the labeled antibodies bind to the antigens on the magnetic beads. The electrons in a benzene ring are delocalised, and this is why all the carbon-carbon bonds are the same length.

Fluorescence: A type of luminescence in which the electrons are excited by light, e. Luminescence: The production of light, usually at low temperatures, for example by chemical reactions or electrical energy. Incandescence, in contrast, is light generated by high temperatures. Phosphorescence: As fluorescence , but the glow lasts for longer according to some definitions, over 10 nanoseconds , for example glow-in-the-dark stickers.

The original version of this article was published in Chemistry Review and is reproduced with kind permission by the publisher, Philip Allan. To subscribe to Chemistry Review , a journal aimed at school chemistry students aged , visit: www.

Download this article as a PDF. Emma Welsh is a freelance science communicator with a PhD in synthetic organic chemistry and postdoctoral experience of medicinal chemistry, making drugs that inhibit enzymes which are involved in cancer biology. This article offers a way to motivate students to understand chemical reactions.

Even if they are not keen to know why a glow stick glows in the dark, they will surely be eager to find out how fireflies or jellyfish produce light, or to discover how blood is detected at crime scenes.

The article can serve either as an introduction to chemical reactions or to give attractive examples of redox reactions and also to illustrate the levels of energy in the shell of an atom. The article can be adapted for different age ranges and for different subjects and topics. For students aged , it could be used to teach chemistry atomic structure and movement of electrons between shells, introduction to chemical reactions or biology bioluminescence.

For this age group, the teacher would need to simplify the information in the article and omit the details of the reactions. For students aged , the article could be used to teach chemistry redox reactions, catalysts, the influence of temperature on reaction speed, the effect of pH on a reaction, and covalent bonds , physics the electromagnetic spectrum and photons or genetics genetic engineering.

Suitable comprehension questions include:. What is chemiluminescence? Understand article. Figure 1: Movement between electron shells A hydrogen atom in its ground state. Each shell has its own energy level. In the process, a packet of energy a photon is released in the form of electromagnetic radiation.

The wavelength depends on the amount of energy. If the wavelength is within the range of visible light, the electron transition will be perceived as light of a particular colour.

The wavelength determines the colour see Figure 2 , below Image courtesy of Chemistry Review. Figure 2: The electromagnetic spectrum. Box 1: Luminol, a glow-in-the-dark chemical The release of a photon of light from a molecule of luminol is a fairly complex, multi-stage process.

Figure 3: Reactions leading to the emission of light from luminol Tautomers are molecules with the same molecular formula, but different arrangements of atoms or bonds.

The two tautomers can be interconverted; the curly arrows show the movement of electrons that brings about the change between the two forms. Click to enlarge image Image courtesy of Chemistry Review. Box 2: Chemistry of glow sticks Click to enlarge image Image courtesy of Chemistry Review When diphenyl oxalate reacts with hydrogen peroxide H 2 O 2 , it is oxidised to give phenol and a cyclic peroxide.

Safety note Phenol is toxic, so if your glow stick leaks, take care not to get the liquid on your hands; if you do, wash them with soapy water straight away. Box 3: What makes glow sticks different colours? Glossary Anion: an atom or group of atoms that bears a negative charge.

The electrons in benzene are delocalised in a conjugated system Image courtesy of Chemistry Review Delocalised: When molecules have conjugated bonds, the electrons are free to move around throughout the entire conjugated system.

Photon: A quantum packet of light energy. Author s Emma Welsh is a freelance science communicator with a PhD in synthetic organic chemistry and postdoctoral experience of medicinal chemistry, making drugs that inhibit enzymes which are involved in cancer biology.

Review This article offers a way to motivate students to understand chemical reactions. Suitable comprehension questions include: What is chemiluminescence? What do forensic scientists use chemiluminescence for? Explain some biological functions of bioluminescence.