Light and Autofluorescence, Multitasking Features in Living Organisms

Abstract

Organisms belonging to all life kingdoms may have the natural capacity to fluoresce. Autofluorescence events depend on the presence of natural biomolecules, namely endogenous fluorophores, with suitable chemical properties in terms of conjugated double bonds, aromatic or more complex structures with oxidized and crosslinked bonds, ensuring an energy status able to permit electronic transitions matching with the energy of light in the UV-visible-near-IR spectral range. Emission of light from biological substrates has been reported since a long time, inspiring unceasing and countless studies. Early notes on autofluorescence of vegetables have been soon followed by attention to animals. Investigations on full living organisms from the wild environment have been driven prevalently by ecological and taxonomical purposes, while studies on cells, tissues and organs have been mainly promoted by diagnostic aims. Interest in autofluorescence is also growing as a sensing biomarker in food production and in more various industrial processes. The associated technological advances have supported investigations ranging from the pure photochemical characterization of specific endogenous fluorophores to their possible functional meanings and biological relevance, making fluorescence a valuable intrinsic biomarker for industrial and diagnostic applications, in a sort of real time, in situ biochemical analysis. This review aims to provide a wide-ranging report on the most investigated natural fluorescing biomolecules, from microorganisms to plants and animals of different taxonomic degrees, with their biological, environmental or biomedical issues relevant for the human health. Hence, some notes in the different sections dealing with different biological subject are also interlaced with human related issues. Light based events in biological subjects have inspired an almost countless literature, making it almost impossible to recall here all associated published works, forcing to apologize for the overlooked reports. This Review is thus proposed as an inspiring source for Readers, addressing them to additional literature for an expanded information on specific topics of more interest.

The Bright Side of the Tiger: Autofluorescence Patterns in Aedes albopictus (Diptera, Culicidae) Male and Female Mosquitoes

“…Early observations on autofluorescence from different biological substrates have paved the way to constant and innumerable studies entailing light based phenomena. Indeed, the direct involvement of endogenous fluorophores in the structure and metabolic functions of cells and tissues, causing them to act as intrinsic biomarkers, is at the basis of the development of diagnostic strategies in biomedicine, as well as of various industrial and analytical procedures with almost countless applications in many areas, from microorganisms to vegetables or animals [ 2 ].…”

Using mass spectrometry to investigate fluorescent compounds in squirrel fur

“…Therefore, fluorescence in mammal fur may require a secondary form of activation or may rely on the accumulation of a specific compound common in mammal fur. There is also growing evidence to suggest that fluorescence in mammals may be the result of either porphyrin or tryptophan synthesis [12,13,36,40,45]. Since we did not find a unique fluorescent compound in flying squirrel fur, it remains possible that fluorescence in flying squirrels is the result of some biochemical pathway involving synthesis of one of these two compounds.…”

“…Perhaps the most enticing aspect of the recent observations of fluorescent mammals is the potential for fluorescent fur to be an adaptive trait. While it remains uncertain, evidence to date suggests that fluorescence in mammals may often be an artefactual result of biochemical synthesis [40,45]. Fluorescence does appear to be an adaptive trait in some taxa, however.…”

Using mass spectrometry to investigate fluorescent compounds in squirrel fur

“…Perhaps the most intriguing aspect of the recent observations of fluorescent mammals is the potential for fluorescent fur to be an adaptive trait. While it remains uncertain, evidence to date suggests that fluorescence in mammals may often be an artefactual result of biochemical synthesis [ 41 , 49 ]. Fluorescence does appear to be an adaptive trait in some taxa, however.…”

“…Second, fluorescence in mammal fur may require a secondary form of activation or reliance on the accumulation of a specific compound common in mammal fur. There is also growing evidence to suggest that fluorescence in mammals may be the result of either porphyrin or tryptophan synthesis [ 12 , 13 , 37 , 42 , 49 ]. Since we did not find a unique fluorescent compound in flying squirrel fur, it remains possible that fluorescence in flying squirrels is the result of some biochemical pathway involving synthesis of one of these two compounds.…”