{{Short description|Natural emission of light by biological structures}} [[Image:PaperAutofluorescence.jpg|thumb|300px|Micrograph of paper autofluorescing under ultraviolet illumination. The individual fibres in this sample are around 10 μm in diameter.]] '''Autofluorescence''' is the natural fluorescence of biological structures ('''autofluorophores''')<ref name=":0">{{Cite journal |last=Campbell |first=Jared M. |last2=Gosnell |first2=Martin |last3=Agha |first3=Adnan |last4=Handley |first4=Shannon |last5=Knab |first5=Aline |last6=Anwer |first6=Ayad G. |last7=Bhargava |first7=Akanksha |last8=Goldys |first8=Ewa M. |date=2024-06-12 |title=Label‐Free Assessment of Key Biological Autofluorophores: Material Characteristics and Opportunities for Clinical Applications |url=https://advanced.onlinelibrary.wiley.com/doi/full/10.1002/adma.202403761 |journal=Advanced Materials |language=en |volume=36 |issue=42 |doi=10.1002/adma.202403761 |issn=0935-9648 |archive-url=http://web.archive.org/web/20250611122824/https://advanced.onlinelibrary.wiley.com/doi/full/10.1002/adma.202403761 |archive-date=2025-06-11|doi-access=free }}</ref> such as mitochondria and lysosomes, in contrast to fluorescence originating from artificially added fluorescent markers (fluorophores).<ref name=Monici-2005> {{cite journal |author=Monici, M. |year=2005 |title=Cell and tissue autofluorescence research and diagnostic applications |journal=Biotechnology Annual Review |volume=11 |pages=227–256 |doi=10.1016/S1387-2656(05)11007-2 |pmid=16216779 |isbn=9780444519528 }} </ref>
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.<ref name=Monici-2005/>
Generally, proteins containing an increased amount of the amino acids tryptophan, tyrosine, and phenylalanine show some degree of autofluorescence.<ref name=Menter-2006/>
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.<ref> {{cite journal |last1=Chia |first1=Thomas |last2=Levene |first2=Michael |date=17 November 2009 |title=Detection of counterfeit U.S. paper money using intrinsic fluorescence lifetime |journal=Optics Express |volume=17 |issue=24 |pages=22054–22061 |doi=10.1364/OE.17.022054 |doi-access=free |pmid=19997451 |bibcode=2009OExpr..1722054C |url=https://zenodo.org/record/894876 }} </ref>
==Microscopy== [[Image:Unmixed Autofluorescence.gif|thumb|300px|A multispectral image of tissue from a mouse intestine, showing how autofluoresce can obscure several fluorescence signals.]] 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. left|thumb|300px|Autofluorescence super resolution microscopy/optical nanoscopy image of cellular structures that are invisible with confocal light microscopy
In a few cases, autofluorescence may actually illuminate the structures of interest, or serve as a useful diagnostic indicator.<ref name=Monici-2005/>
For example, cellular autofluorescence can be used as an indicator of cytotoxicity without the need to add fluorescent markers.<ref name="Fri10">{{cite journal |author1=Fritzsche, M. |author2=Mandenius, C.F. |date=September 2010 |title=Fluorescent cell-based sensing approaches for toxicity testing |journal=Anal Bioanal Chem |volume=398 |issue=1 |pages=181–191 |pmid=20354845 |s2cid=22712460 |doi=10.1007/s00216-010-3651-6 }} </ref>
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.<ref name="Ger09"> {{cite journal |author1=Gerrits, E.G. |author2=Smit, A.J. |author3=Bilo, H.J. |date=March 2009 |title=AGEs, autofluorescence and renal function |journal=Nephrol. Dial. Transplant. |volume=24 |issue=3 |pages=710–713 |pmid=19033250 |doi=10.1093/ndt/gfn634 |doi-access=free }} </ref> [[File:BananaSkin40X_Fluorescence.tif|thumb|220px|right|Autofluorescence in banana skin under different light conditions.]]
Optical imaging systems that utilize multispectral imaging can reduce signal degradation caused by autofluorescence while adding enhanced multiplexing capabilities.<ref>{{cite journal | url=https://dx.doi.org/10.1117/1.2032458 | doi=10.1117/1.2032458 | title=Autofluorescence removal, multiplexing, and automated analysis methods for in-vivo fluorescence imaging | date=2005 | last1=Mansfield | first1=James R. | last2=Gossage | first2=Kirk W. | last3=Hoyt | first3=Clifford C. | last4=Levenson | first4=Richard M. | journal=Journal of Biomedical Optics | volume=10 | issue=4 | page=041207 | pmid=16178631 | bibcode=2005JBO....10d1207M | s2cid=35269802 | doi-access=free }}</ref>
The super resolution microscopy SPDM revealed autofluorescent cellular objects which are not detectable under conventional fluorescence imaging conditions.<ref> {{cite journal | author1 = Kaufmann, R. | author2 = Müller, P. | author3 = Hausmann, M. | author4 = Cremer, C. | year = 2010 | title = Imaging label-free intracellular structures by localisation microscopy | journal = Micron | volume = 42 | issue = 4 | pages = 348–352 | doi = 10.1016/j.micron.2010.03.006 | pmid = 20538472 }} </ref>
==List of dominant autofluorophores== :{| class="wikitable sortable" style="text-align:center;" |- style="vertical-align:bottom;" !Group ! Molecule ! Excitation<br/>(nm) ! Fluorescence<br/>(nm) Peak ! {{vertical header| '''Animals''' (Zoae) }} <!-- "Z" for zoae / metazoae --> ! {{vertical header| '''Fungi''' }} <!-- "F" --> ! {{vertical header| '''Plants''' }} <!-- "P" --> <!-- ! {{vertical header| '''Archea''' }} < !-- "A" -- > ! {{vertical header| '''Bacteria''' }} < !-- "B" -- > --> ! {{vertical header| '''Reference''' }} |- | | NAD(P)H | 340 | 450 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| '''{{sc|F}}''' |style="text-align:center;"| '''{{sc|P}}''' <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | <ref name=Georgakoudi-Jacobson-etal-2002-02-01> <!-- former ref name=nad --> {{cite journal |author1=Georgakoudi, I. |author2=Jacobson, B.C. |author3=Müller, M.G. |author4=Sheets, E.E. |author5=Badizadegan K. |author6=Carr-Locke, D.L. |author7=Crum, C.P. |author8=Boone, C.W. |author9=Dasari, R.R. |author10=van Dam, J. |author11=Feld, MS |display-authors=6 |date=2002-02-01 |title=NAD(P)H and collagen as ''in vivo'' quantitative fluorescent biomarkers of epithelial precancerous changes |journal=Cancer Research |volume=62 |issue=3 |pages=682–687 |pmid= 11830520 }} </ref> |- | | Chlorophyll | 465–665 | 673–726 |style="text-align:center;"| |style="text-align:center;"| |style="text-align:center;"| '''{{sc|P}}''' <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | |- | |Collagen | 270–370 | 305–450 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| |style="text-align:center;"| <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | <ref name=Georgakoudi-Jacobson-etal-2002-02-01/> |- | | Retinol | | 500 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| '''{{sc|F}}''' |style="text-align:center;"| '''{{sc|P}}''' <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | <ref name=Zipfel-Williams-etal-2003-06-10> <!-- former ref name=liv --> {{cite journal |author1=Zipfel, W.R. |author2=Williams, R.M. |author3=Christie, R. |author4=Nikitin, A.Y. |author5=Hyman, B.T. |author6=Webb, W.W. |date=2003-06-10 |title=Live tissue intrinsic emission microscopy using multiphoton-excited native fluorescence and second harmonic generation |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=100 |issue=12 |pages=7075–7080 |doi=10.1073/pnas.0832308100 |doi-access=free |pmc=165832 |pmid=12756303 |bibcode=2003PNAS..100.7075Z }} </ref> |- | | Riboflavin | | 550 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| '''{{sc|F}}''' |style="text-align:center;"| '''{{sc|P}}''' <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | <ref name=Zipfel-Williams-etal-2003-06-10/> |- | | Cholecalciferol | | 380–460 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| |style="text-align:center;"| <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | <ref name=Zipfel-Williams-etal-2003-06-10/> |- | | Folic acid | | 450 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| '''{{sc|F}}''' |style="text-align:center;"| '''{{sc|P}}''' <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | <ref name=Zipfel-Williams-etal-2003-06-10/> |- | | Pyridoxine | | 400 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| '''{{sc|F}}''' |style="text-align:center;"| '''{{sc|P}}''' <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | <ref name=Zipfel-Williams-etal-2003-06-10/> |- | | Tyrosine | 270 | 305 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| '''{{sc|F}}''' |style="text-align:center;"| '''{{sc|P}}''' <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | <ref name=Menter-2006> {{cite journal |author=Menter, Julian M. |year=2006 |title=Temperature dependence of collagen fluorescence |journal= Photochemical & Photobiological Sciences |volume=5 |issue=4 |pages=403–410 |pmid=16583021 |doi=10.1039/b516429j |s2cid=34205474 }} </ref> |- | | Dityrosine | 325 | 400 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| |style="text-align:center;"| <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | <ref name=Menter-2006/> |- | | Excimer-like<br/>aggregate<br/>(collagen) | 270 | 360 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| |style="text-align:center;"| <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | <ref name=Menter-2006/> |- | | Glycation adduct | 370 | 450 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| |style="text-align:center;"| <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | <ref name=Menter-2006/> |- | | Indolamine | | |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| |style="text-align:center;"| <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | |- | | Lipofuscin | 410–470 | 500–695 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| '''{{sc|F}}''' |style="text-align:center;"| '''{{sc|P}}''' <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | <ref name=Schönenbrücher-etal-2008> {{cite journal |author1=Schönenbrücher, Holger |author2=Adhikary, Ramkrishna |author3=Mukherjee, Prasun |author4=Casey, Thomas |author5=Rasmussen, Mark |author6=Maistrovich, Frank |author7=Hamir, Amir |author8=Kehrli, Marcus |author9=Richt, Jurgen |author10=Petrich, Jacob |display-authors=6 |year=2008 |title=Fluorescence-based method, exploiting lipofuscin, for real-time detection of central nervous system tissues on bovine carcasses |journal=Journal of Agricultural and Food Chemistry |volume=56 |issue=15 |pages=6220–6226 |doi=10.1021/jf0734368 |pmid=18620407 |url=https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1548&context=chem_pubs }} </ref> |- | | Lignin<br/>(a polyphenol) | 335–488 | 455–535 |style="text-align:center;"| |style="text-align:center;"| |style="text-align:center;"| '''{{sc|P}}''' <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | <ref> {{cite journal |author1=Donaldson, Lloyd |author2=Williams, Nari |date=February 2018 |title=Imaging and spectroscopy of natural fluorophores in pine needles |journal=Plants |volume=7 |issue=1 |page=10 |doi=10.3390/plants7010010 |doi-access=free |pmid=29393922 |pmc=5874599 }} </ref> |- | | Tryptophan | 280 | 300–350 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| '''{{sc|F}}''' |style="text-align:center;"| '''{{sc|P}}''' <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | |- | |Flavin | 380–490 | 520–560 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| '''{{sc|F}}''' |style="text-align:center;"| '''{{sc|P}}''' <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | |- | | Melanin | 340–400 | 360–560 |style="text-align:center;"| '''{{sc|Z}}''' |style="text-align:center;"| '''{{sc|F}}''' |style="text-align:center;"| '''{{sc|P}}''' <!-- |style="text-align:center;"| '''{{sc|A}}''' |style="text-align:center;"| '''{{sc|B}}''' --> | <ref name=Gallas-Eisner-1987-05> {{cite journal |author1=Gallas, James M. |author2=Eisner, Melvin |name-list-style=amp |date=May 1987 |title=Fluorescence of melanin-dependence upon excitation wavelength and concentration |journal= Photochemistry and Photobiology |volume=45 |issue=5 |pages=595–600 |doi=10.1111/j.1751-1097.1987.tb07385.x |s2cid=95703924 }} </ref> |- | rowspan="4" |Nicotinamides |Unbound NADH | rowspan="2" |250–300 and 300–380 | rowspan="2" |420–480 | style="text-align: center;" | | | | rowspan="21" |<ref name=":0" /> |- |Unbound NADPH | | | |- |Protein-bound NADH | rowspan="2" |Blue shifts ≈20 nm compared to its unbound form | rowspan="2" |Blue shifts ≈20 nm compared to unbound form | | | |- |Protein-bound NADPH | | | |- | rowspan="3" |Flavins |Riboflavin (Vitamin B2) | rowspan="3" |210–290 and 325–490 | rowspan="3" |480–625 and 490–600 | | | |- |Flavin mononucleotide (FMN) | | | |- |Flavin adenine dinucleotide (FAD<sup>+</sup>) | | | |- |Collagens |Types 1-28 |250–450<ref name=":1">Diverse results in literature varying with type, structure, and preparation method</ref> |250–550<ref name=":1" /> | | | |- | rowspan="2" |Porphyrins |Coproporphyrin I |≈360–440 |580–730 | | | |- |Protoporphyrin IX |350–650 |580–730 | | | |- | rowspan="3" |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 | | | |- | rowspan="3" |Retinols |Retinol |250–380 |414–550 | | | |- |Retinol-binding protein (RBP) bound to retinol | rowspan="2" |260–400 |250–575 | | | |- |Unbound RBP |250–575 | | | |}
:{{small| Substances luminous in animal tissue are, by taxonomic inclusion, also luminous in human tissue.}}
==See also== * Autoluminescence * Phosphorescence * Fluorescence in the life sciences
==References== {{reflist}}
Category:Microscopy