In this post we will cover in detail chemiluminescence definition and many chemiluminescence examples. The Chemiluminescence definition is the release of light from a chemical reaction. The light is released either from a high-energy intermediate itself or when a high-energy intermediate relaxes down to the lower energy final product. It is important to remember that chemiluminesence is the result of a chemical reaction, and is not the same as fluorescence. This means that chemiluminescent reactions do not need an input of excitation light of any kind. The overriding chemical formula of chemiluminescent reactions is A + B→ C* + D → C + light + D
Where C* is the high energy intermediate.
Probably one of the most well-known chemiluminescence examples is the reaction of luciferin with ATP in the presence of the enzyme luciferase. This is the reaction that occurs within fireflies to produce their light. This reaction could be categorized as bioluminescence. An adaptation to this reaction was made for use in the laboratory where peroxidase is used in place of luciferase as the catalyzing enzyme. Enzyme protectors such as phenols, napthols, aromatic amines, or benzothiazoles are added to the reaction to preserve the enzyme and enhance the light output over several minutes. For this reason these molecules are called “enhancers”.
Another chemiluminescence examples is that of luminol with hydrogen peroxide. This reaction ia catalyzed by the iron located in haemoglobin. 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 examples 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 9,10-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.
Chemiluminescent examples: magnetic immunoassay
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. Then, the conjugated beads are isolated from solution by magnetic separation. After isolation the reaction solution is added. This reaction solution contains the other substrate and an appropriate enzyme to produce a chemiluminescent reaction. Light is produced only if the labeled antibodies matched the antigens on the bead surface.