Introduction and History

Luminescent organisms have been observed throughout the ages. The cause of the luminescence wasn’t known until the advent of the microscope and modern science. In the oceans, sailors often remarked at the eerie glowing water generated by their vessels. Christopher Columbus, during his historic voyage across the Atlantic, noticed mysterious patches of luminescent light around the waters of his ships (Floyd, 1997). Often, the explanations of the luminescence found in the oceans were attributed to monsters of the deep or other mysteries of the unknown. During the era of great Greek philosophers, Aristotle and Pliny had noticed that the flesh of dead fish and damp wood appear to luminesce (Harvey, 1920). The first serious scientific attempts to understand the origin of luminescence in organisms were underway by the mid 1600’s. Not knowing the exact reason why, Boyle, using air pumps, determined that luminescence of dead flesh and fungi was dependent on the air (oxygen) (Kruse, 2000; Harvey, 1952). However, it wasn’t until the 1830’s when the German scientist, G. A. Michaelis, discovered that the luminescence from dead fish was due to something living (Harvey, 1920). The French physiologist Raphael Dubois, in 1885, was the first to isolate the light producing chemicals from clams (Alcamo, 2003; Harvey, 1920), which paved the way for the characterization of the molecular, chemical, and physiological mechanisms behind this process. Today, bioluminescence has been observed in thousands of species including bacteria, fungi, and marine animals. Only within the last 20 years has bioluminescence been harnessed as a scientific tool. Today, bioluminescence is being applied directly in experimental assays and attempts are being made to mass market bioluminescence to the general public. What is Bioluminescence? Bioluminescence belongs to a family of terms (including fluorescence, phosphorescence, and chemiluminescence) referring to the production of light chemicals. In fluorescence, energy, typically light of given wavelength, from an outside source interacts and excites a fluorophore – a substance that undergoes fluorescence. The energy becomes absorbed and creates an unstable “energized” fluorophore. In the attempts to regain stability, the “energized” fluorophore immediately releases the extra energy as light at a longer wavelength (Haddock et al., 2000). Once the excitation energy is removed the fluorescence is stopped. Phosphorescence is based on a similar principle to fluorescence. However, the light emitted lasts longer because of the greater stability of the energized phosphorescent substance (Haddock et al., 2000), even after the removal of the energy source. Examples of common phosphorescent products are glow-in-the-dark stickers and glow-in-the-dark facets found on watches. Chemiluminescence is based on the principle of fluorescence but the energy required to generate light comes from a chemical reaction. Unlike a burning candle, which generates light and heat, chemiluminescence, fluorescence, and phosphorescence generates little to no heat. Bioluminescence refers to light generated from within an organism. The generated light can be formed by either fluorescence or chemiluminescence and involves the use of proteins. Bioluminescence due to chemiluminescence commonly uses the enzyme “luciferase” to catalyze the oxidation of a substrate “luciferin” generating light as a by-product. Bioluminescence due to fluorescence requires an accessory protein, a fluorophore that requires the light energy generated from chemiluminescence in order to generate light.