Autofluorescence is the natural emission of light by biological structures such as mitochondria and lysosomes when they have absorbed light, and is used to distinguish the light originating from artificially added fluorescent markers (fluorophores).[1]
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.[1]
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.[3]
Microscopyedit
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.[1]
For example, cellular autofluorescence can be used as an indicator of cytotoxicity without the need to add fluorescent markers.[4]
The super resolution microscopySPDM revealed autofluorescent cellular objects which are not detectable under conventional fluorescence imaging conditions.[7]
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Monici, M. (2005). "Cell and tissue autofluorescence research and diagnostic applications". Biotechnology Annual Review. 11: 227–256. doi:10.1016/S1387-2656(05)11007-2. ISBN 9780444519528. PMID 16216779.
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Chia, Thomas; Levene, Michael (17 November 2009). "Detection of counterfeit U.S. paper money using intrinsic fluorescence lifetime". Optics Express. 17 (24): 22054–22061. Bibcode:2009OExpr..1722054C. doi:10.1364/OE.17.022054. PMID 19997451.
^Mansfield, James R.; Gossage, Kirk W.; Hoyt, Clifford C.; Levenson, Richard M. (2005). "Autofluorescence removal, multiplexing, and automated analysis methods for in-vivo fluorescence imaging". Journal of Biomedical Optics. 10 (4): 041207. Bibcode:2005JBO....10d1207M. doi:10.1117/1.2032458. PMID 16178631. S2CID 35269802.
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Kaufmann, R.; Müller, P.; Hausmann, M.; Cremer, C. (2010). "Imaging label-free intracellular structures by localisation microscopy". Micron. 42 (4): 348–352. doi:10.1016/j.micron.2010.03.006. PMID 20538472.
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Georgakoudi, I.; Jacobson, B.C.; Müller, M.G.; Sheets, E.E.; Badizadegan K.; Carr-Locke, D.L.; et al. (2002-02-01). "NAD(P)H and collagen as in vivo quantitative fluorescent biomarkers of epithelial precancerous changes". Cancer Research. 62 (3): 682–687. PMID 11830520.
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Zipfel, W.R.; Williams, R.M.; Christie, R.; Nikitin, A.Y.; Hyman, B.T.; Webb, W.W. (2003-06-10). "Live tissue intrinsic emission microscopy using multiphoton-excited native fluorescence and second harmonic generation". Proceedings of the National Academy of Sciences of the United States of America. 100 (12): 7075–7080. Bibcode:2003PNAS..100.7075Z. doi:10.1073/pnas.0832308100. PMC165832. PMID 12756303.
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Schönenbrücher, Holger; Adhikary, Ramkrishna; Mukherjee, Prasun; Casey, Thomas; Rasmussen, Mark; Maistrovich, Frank; et al. (2008). "Fluorescence-based method, exploiting lipofuscin, for real-time detection of central nervous system tissues on bovine carcasses". Journal of Agricultural and Food Chemistry. 56 (15): 6220–6226. doi:10.1021/jf0734368. PMID 18620407.
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Donaldson, Lloyd; Williams, Nari (February 2018). "Imaging and spectroscopy of natural fluorophores in pine needles". Plants. 7 (1): 10. doi:10.3390/plants7010010. PMC5874599. PMID 29393922.
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Gallas, James M. & Eisner, Melvin (May 1987). "Fluorescence of melanin-dependence upon excitation wavelength and concentration". Photochemistry and Photobiology. 45 (5): 595–600. doi:10.1111/j.1751-1097.1987.tb07385.x. S2CID 95703924.