Autofluorescence
Natural emission of light by biological structures
From Wikipedia, the free encyclopedia
Autofluorescence is the natural fluorescence of biological structures (autofluorophores)[1] such as mitochondria and lysosomes, in contrast to fluorescence originating from artificially added fluorescent markers (fluorophores).[2]
The most commonly observed autofluorescencing molecules are NADPH and flavins; the extracellular matrix can also contribute to autofluorescence because of the intrinsic properties of collagen and elastin.[2]
Generally, proteins containing an increased amount of the amino acids tryptophan, tyrosine, and phenylalanine show some degree of autofluorescence.[3]
Autofluorescence also occurs in non-biological materials found in many papers and textiles. Autofluorescence from U.S. paper money has been demonstrated as a means for discerning counterfeit currency from authentic currency.[4]
Microscopy
Autofluorescence can be problematic in fluorescence microscopy. Light-emitting stains (such as fluorescently labelled antibodies) are applied to samples to enable visualisation of specific structures.
Autofluorescence interferes with detection of specific fluorescent signals, especially when the signals of interest are very dim — it causes structures other than those of interest to become visible.
In some microscopes (mainly confocal microscopes), it is possible to make use of different lifetime of the excited states of the added fluorescent markers and the endogenous molecules to exclude most of the autofluorescence.
In a few cases, autofluorescence may actually illuminate the structures of interest, or serve as a useful diagnostic indicator.[2]
For example, cellular autofluorescence can be used as an indicator of cytotoxicity without the need to add fluorescent markers.[5]
The autofluorescence of human skin can be used to measure the level of advanced glycation end-products (AGEs), which are present in higher quantities during several human diseases.[6]
Optical imaging systems that utilize multispectral imaging can reduce signal degradation caused by autofluorescence while adding enhanced multiplexing capabilities.[7]
The super resolution microscopy SPDM revealed autofluorescent cellular objects which are not detectable under conventional fluorescence imaging conditions.[8]
List of dominant autofluorophores
Group Molecule Excitation
(nm)Fluorescence
(nm) PeakAnimals (Zoae)FungiPlantsReferenceNAD(P)H 340 450 Z F P [9] Chlorophyll 465–665 673–726 P Collagen 270–370 305–450 Z [9] Retinol 500 Z F P [10] Riboflavin 550 Z F P [10] Cholecalciferol 380–460 Z [10] Folic acid 450 Z F P [10] Pyridoxine 400 Z F P [10] Tyrosine 270 305 Z F P [3] Dityrosine 325 400 Z [3] Excimer-like
aggregate
(collagen)270 360 Z [3] Glycation adduct 370 450 Z [3] Indolamine Z Lipofuscin 410–470 500–695 Z F P [11] Lignin
(a polyphenol)335–488 455–535 P [12] Tryptophan 280 300–350 Z F P Flavin 380–490 520–560 Z F P Melanin 340–400 360–560 Z F P [13] Nicotinamides Unbound NADH 250–300 and 300–380 420–480 [1] Unbound NADPH Protein-bound NADH Blue shifts ≈20 nm compared to its unbound form Blue shifts ≈20 nm compared to unbound form Protein-bound NADPH Flavins Riboflavin (Vitamin B2) 210–290 and 325–490 480–625 and 490–600 Flavin mononucleotide (FMN) Flavin adenine dinucleotide (FAD+) Collagens Types 1-28 250–450[14] 250–550[14] Porphyrins Coproporphyrin I ≈360–440 580–730 Protoporphyrin IX 350–650 580–730 Aromatic amino acids Tyrosine 250–325 300–400 and 500–600 Tryptophan 250–310 300–425 Dityrosine 250–350 350–410 Elastin 300–480 450–650 A2E 250–550 500–750 Lipofuscin 320–480 400–700 Melanin 350–600 450–800 Keratin 365–460 410–600 Retinols Retinol 250–380 414–550 Retinol-binding protein (RBP) bound to retinol 260–400 250–575 Unbound RBP 250–575
- Substances luminous in animal tissue are, by taxonomic inclusion, also luminous in human tissue.