Chemoluminescence
- Bioluminescence

A chemoluminescent reaction carried out in an erlenmeyer flask producing a large amount of light.Chemoluminescence (sometimes "chemiluminescence") is the emission of light (luminescence) as the result of a chemical reaction. Most simply, given reactants A and B, with an excited intermediate ◊, we have,

[A] + [B] → [◊] → [Products] + light

The decay of the excited state[◊] to a lower energy level is responsible for the emission of light. In theory, one photon of light should be given off for each molecule of reactant, or Avogadro's number of photons per mole. In actual practice, non-enzymatic reactions seldom exceed 1% Q_C, quantum efficiency.For example, if [A] is luminol and [B] is hydrogen peroxide in the presence of a suitable catalyst we have,

luminol + H₂O₂ → 3-APA[◊] → 3-APA + light

Where 3-APA is 3-aminophthalate. And 3-APA[◊] is the excited state fluorescing as it decays to a lower energy level. A standard example of chemiluminescence in the laboratory setting is found in the luminol test, where evidence of blood is taken when the sample glows upon contact with iron. When chemoluminescence takes place in living organisms, the phenomenon is called bioluminescence. A glowstick emits light by chemoluminescence.

Bioluminescence

Chemoluminescence takes place in numerous living organisms, the American firefly being a widely studied case of bioluminescence.The firefly reaction has the highest known quantum efficiency, Q_C of 88%, for chemoluminescence reactions. ATP (adenosine tri-phosphate), the ubiquitous biological energy source, reacts with luciferin with the aid of the enzyme luciferase to yield an intermediate complex. This complex combines with oxygen to produce a highly fluorescent compound.Quantum efficiency (QE) is a quantity defined for a photosensitive device such as photographic film or a charge-coupled device (CCD) as the percentage of photons hitting the photoreactive surface that will produce an electron–hole pair. It is an accurate measurement of the device's sensitivity. It is often measured over a range of different wavelengths to characterize a device's efficiency at each energy. Photographic film typically has a QE of much less than 10%, while CCDs can have a QE of well over 90% at some wavelengths.

To convert from responsivity to QE in %: QE = [(R x 1240)/λ] x 100

where R is the responsivity in A/W at the wavelength λ, and λ, the wavelength, is in nm.

Luciferins (from the Latin lucifer, "light-bringing") are a class of light-emitting biological pigments found in organisms capable of bioluminescence.Note that luciferins should not be confused with the enzyme luciferase. Luciferins are a substrate for luciferase. Luciferins are oxidized in the presence of the enzyme luciferase to produce oxyluciferin and energy in the form of light. There are five general types of luciferins.

Firefly luciferin

Firefly luciferin is the luciferin found in fireflies. It is the substrate of luciferase.

Bacterial luciferin

Bacterial luciferin is a type of luciferin found in bacteria, some squids and fishes. It consists of a long-chain aldehyde and a reduced riboflavin phosphate.

Dinoflagellate luciferin

Dinoflagellate luciferin is a chlorophyll derivative and is found in dinoflagellates, which are often responsible for the phenomenon of nighttime ocean phosphorescence. A very similar type of luciferin is found in some types of euphausiid shrimp.LuciferaseLuciferase is a generic name for enzymes commonly used in nature for bioluminescence. The name itself is derived from Lucifer, which means light-bearer. The most famous one is firefly luciferase (EC 1.13.12.7) from the firefly Photinus pyralis. In luminescent reactions, light is produced by the oxidation of a luciferin (a pigment), sometimes involving Adenosine triphosphate (ATP). The rates of this reaction between luciferin and oxygen are extremely slow until they are catalyzed by luciferase, often mediated by the presence of calcium ions (an analog of muscle contraction)^[1]. The reaction takes place in two steps:

Luciferin + ATP → Luciferyl adenylate + PPi

Luciferyl adenylate + O₂ → Oxyluciferin + AMP + Light

The reaction is very energy efficient: nearly all of the energy input into the reaction is transformed into light. As a comparison, the incandescent light bulb loses about 90% of its energy to heat.Luciferin and luciferase are not specific molecules. They are generic terms for a substrate and its associated enzyme (or protein) that catalyze a light-producing reaction. A variety of species regulate their light production using a luciferase. The most famous is the firefly, although it exists in organisms as different as the Jack-O-Lantern mushroom and many marine creatures. In the firefly, the oxygen required is supplied through a tube in the abdomen called the abdominal trachea. Some organisms, notably the click beetles, have several different luciferase enzymes, which each can produce different colors from the same luciferin.