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| [[File:FRET Jabolinski Diagram.svg|thumb|Jablonski diagram of FRET with typical timescales indicated.]] '''Förster resonance energy transfer''' ('''FRET'''), '''Fluorescence resonance energy transfer''' ('''FRET'''), '''resonance energy transfer''' ('''RET''') or '''electronic energy transfer''' ('''EET'''), is a mechanism describing energy transfer between two [[chromophore]]s.<ref>{{cite book |first1=Ping-Chin |last1=Cheng |chapter=The Contrast Formation in Optical Microscopy |chapterurl=http://books.google.com/books?id=E2maxdEXFNoC&pg=PA162 |pages=162–206 |editor1-last=Pawley |editor1-first=James B. |title=Handbook Of Biological Confocal Microscopy |year=2006 |publisher=Springer |location=New York, NY |isbn=978-0-387-25921-5 |edition=3rd |doi=10.1007/978-0-387-45524-2_8}}</ref> A donor chromophore, initially in its electronic excited state, may transfer energy to an acceptor chromophore through nonradiative [[dipole–dipole coupling]].<ref>{{cite book |last=Helms |first=Volkhard |chapter=Fluorescence Resonance Energy Transfer |chapterurl=http://books.google.com/books?id=-Tavvybv5UwC&pg=PA202 |title=Principles of Computational Cell Biology |year=2008 |publisher=Wiley-VCH |location=Weinheim |isbn=978-3-527-31555-0 |page=202}}</ref> The efficiency of this energy transfer is inversely proportional to the sixth power of the distance between donor and acceptor making FRET extremely sensitive to small distances.<ref>{{cite book |last=Harris |first=Daniel C. |chapter=Applications of Spectrophotometry |chapterurl=http://books.google.com/books?id=kIgLJ1De_jwC&pg=PA419 |title=Quantitative Chemical Analysis |year=2010 |publisher=W. H. Freeman and Co. |location=New York |isbn=978-1-4292-1815-3 |pages=419–44 |edition=8th}}</ref>
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| Measurements of FRET efficiency can be used to determine if two fluorophores are within a certain distance of each other.<ref>{{cite book |last=Zheng |first=Jie |chapter=Spectroscopy-Based Quantitative Fluorescence Resonance Energy Transfer Analysis |chapterurl=http://books.google.com/books?id=Q2k-T_1DPcwC&pg=PA65 |title=Ion Channels: Methods and Protocols |series=Methods in Molecular Biology, Volume 337 |year=2006 |publisher=Humana Press |location=Totowa, NJ |isbn=978-1-59745-095-9 |pages=65–77 |editor1-first=James D. |editor1-last=Stockand |editor2-first=Mark S. |editor2-last=Shapiro |doi=10.1385/1-59745-095-2:65}}</ref> Such measurements are used as a research tool in fields including biology and chemistry.
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| FRET is analogous to [[Near and far field|near field]] [[Near Field Communication|communication]], in that the radius of interaction is much smaller than the [[Light|wavelength]] of light emitted. In the [[near and far field|near field]] region, the excited chromophore emits a [[virtual photon]] that is instantly absorbed by a receiving chromophore. These virtual photons are undetectable, since their existence violates the conservation of energy and momentum, and hence FRET is known as a ''radiationless'' mechanism. [[quantum electrodynamics|Quantum electrodynamical]] calculations have been used to determine that radiationless (FRET) and [[radiative transfer|radiative energy transfer]] are the short- and long-range [[asymptote]]s of a single unified mechanism.<ref>{{cite journal |doi=10.1016/0301-0104(89)87019-3 |title=A unified theory of radiative and radiationless molecular energy transfer |year=1989 |last1=Andrews |first1=David L |journal=Chemical Physics |volume=135 |issue=2 |pages=195–201 |bibcode=1989CP....135..195A}}</ref><ref>{{cite journal |doi=10.1088/0143-0807/25/6/017 |title=Virtual photons, dipole fields and energy transfer: A quantum electrodynamical approach |year=2004 |last1=Andrews |first1=David L |last2=Bradshaw |first2=David S |journal=European Journal of Physics |volume=25 |issue=6 |pages=845–58}}</ref>
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| ==Terminology==
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| Förster resonance energy transfer is named after the German scientist [[Theodor Förster]].<ref>{{cite journal |doi=10.1002/andp.19484370105 |title=Zwischenmolekulare Energiewanderung und Fluoreszenz |trans_title=Intermolecular energy migration and fluorescence |year=1948 |last1=Förster |first1=Theodor |journal=Annalen der Physik |volume=437 |bibcode=1948AnP...437...55F |pages=55–75 |language=German}}</ref> When both chromophores are fluorescent, the term "fluorescence resonance energy transfer" is often used instead, although the energy is not actually transferred by [[Fluorescence in the life sciences|fluorescence]].<ref>{{cite book |first1=Bernard |last1=Valeur |first2=Mario |last2=Berberan-Santos |chapter=Excitation Energy Transfer|title=Molecular Fluorescence: Principles and Applications, 2nd ed. |year=2012 |publisher=Wiley-VCH |location=Weinheim |isbn=9783527328376 |pages=213–261 |doi=10.1002/9783527650002.ch8}}</ref><ref>[http://www.olympusfluoview.com/applications/fretintro.html FRET microscopy tutorial from Olympus]</ref> In order to avoid an erroneous interpretation of the phenomenon that is always a nonradiative transfer of energy (even when occurring between two fluorescent chromophores), the name "Förster resonance energy transfer" is preferred to "fluorescence resonance energy transfer;" however, the latter enjoys common usage in scientific literature.<ref>{{cite book |title=Glossary of Terms Used in Photochemistry |edition=3rd |year=2007 |publisher=IUPAC |page=340}}</ref>
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| ==Theoretical basis==
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| The FRET efficiency (<math>E</math>) is the [[quantum yield]] of the energy transfer transition, ''i.e.'' the fraction of energy transfer event occurring per donor excitation event:<ref>{{cite web|last=Moens|first=Pierre|title=Fluorescence Resonance Energy Transfer spectroscopy|url=http://www.anatomy.usyd.edu.au/mru/fret/abot.html#frete|accessdate=July 14, 2012}}</ref>
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| : <math>E = \frac{k_{ET}}{k_f+k_{ET}+\sum{k_i}}</math>
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| where <math>k_{ET}</math> is the rate of energy transfer, <math>k_{f}</math> the radiative decay rate, and the <math>k_{i}</math>'s are the rate constants of any other de-excitation pathways.<ref name=SchaufeleDemarcoDay2005p72-94>{{cite book |first1=Fred |last1=Schaufele |first2=Ignacio |last2=Demarco |first3=Richard N. |last3=Day |chapter=FRET Imaging in the Wide-Field Microscope |chapterurl=http://books.google.com/books?id=K0aawJ6sX-sC&pg=PA72 |pages=72–94 |editor1-first=Ammasi |editor1-last=Periasamy |editor2-first=Richard |editor2-last=Day |year=2005 |title=Molecular Imaging: FRET Microscopy and Spectroscopy |publisher=Oxford University Press |location=Oxford |isbn=978-0-19-517720-6 |doi=10.1016/B978-019517720-6.50013-4}}</ref>
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| The FRET efficiency depends on many physical parameters that can be grouped as follows:
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| * The distance between the donor and the acceptor (typically in the range of 1-10 nm)
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| * The spectral overlap of the donor [[emission spectrum]] and the acceptor [[absorption spectrum]].
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| * The relative orientation of the donor emission dipole moment and the acceptor absorption dipole moment.
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| <math>E</math> depends on the donor-to-acceptor separation distance <math>r</math> with an inverse 6th power law due to the dipole-dipole coupling mechanism:
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| : <math>E=\frac{1}{1+(r/R_0)^6}\!</math>
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| with <math>R_0</math> being the Förster distance of this pair of donor and acceptor, i.e. the distance at which the energy transfer efficiency is 50%.<ref name=SchaufeleDemarcoDay2005p72-94/>
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| The Förster distance depends on the overlap [[integral]] of the donor emission spectrum with the acceptor absorption spectrum and their mutual molecular orientation as expressed by the following equation.<ref>{{cite book | last1 = Förster | first1 = Th. | title = Modern Quantum Chemistry. Istanbul Lectures. Part III: Action of Light and Organic Crystals | chapter = Delocalized Excitation and Excitation Transfer | volume = 3 | editor1-first = Oktay | editor1-last = Sinanoglu | publisher = Academic Press | year = 1965 | location = New York and London | pages = 93–137 | url = http://www.quantum-chemistry-history.com/Sina_Dat/BOOKIstaLec/IstaLec1.htm | accessdate = 2011-06-22}}</ref><ref name=Clegg2009p1-57>{{cite book |last=Clegg |first=Robert |title=FRET and FLIM Techniques |series=Laboratory Techniques in Biochemistry and Molecular Biology, Volume 33 |year=2009 |publisher=Elsevier |isbn=978-0-08-054958-3 |editor1-first=Theodorus W. J. |editor1-last=Gadella |chapter=Förster resonance energy transfer—FRET: what is it, why do it, and how it's done |chapterurl=http://books.google.com/books?id=uHvqu4hLhH8C&pg=PA1 |pages=1–57 |doi=10.1016/S0075-7535(08)00001-6}}</ref>
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| : <math> {R_0}^6 = \frac{9\,Q_0 \,(\ln 10) \kappa^2 \, J}{128 \, \pi^5 \,n^4 \, N_A} </math> | |
| where <math>Q_0</math> is the fluorescence [[quantum yield]] of the donor in the absence of the acceptor, ''κ''<sup>2</sup> is the dipole orientation factor, <math>n</math> is the [[refractive index]] of the medium, <math>N_A</math> is [[Avogadro's number]], and <math>J</math> is the spectral overlap integral calculated as
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| : <math> J = \int f_{\rm D}(\lambda) \, \epsilon_{\rm A}(\lambda) \, \lambda^4 \, d\lambda </math>
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| where <math>f_{\rm D}</math> is the normalized donor emission spectrum, and <math>\epsilon_{\rm A}</math> is the acceptor [[molar extinction coefficient]].<ref name="Demchenko2008">{{cite book |last=Demchenko |first=Alexander P. |chapter=Fluorescence Detection Techniques |chapterurl=http://books.google.com/books?id=wMARxPxkE7EC&pg=PA65 |title=Introduction to Fluorescence Sensing |year=2008 |publisher=Springer |location=Dordrecht |isbn=978-1-4020-9002-8 |pages=65–118 |doi=10.1007/978-1-4020-9003-5_3}}</ref>
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| ''κ''<sup>2</sup> =2/3 is often assumed. This value is obtained when both dyes are freely rotating and can be considered to be isotropically oriented during the excited state lifetime. If either dye is fixed or not free to rotate, then ''κ''<sup>2</sup> =2/3 will not be a valid assumption. In most cases, however, even modest reorientation of the dyes results in enough orientational averaging that ''κ''<sup>2</sup> = 2/3 does not result in a large error in the estimated energy transfer distance due to the sixth power dependence of ''R''<sub>0</sub> on ''κ''<sup>2</sup>. Even when ''κ''<sup>2</sup> is quite different from 2/3 the error can be associated with a shift in ''R''<sub>0</sub> and thus determinations of changes in relative distance for a particular system are still valid. Fluorescent proteins do not reorient on a timescale that is faster than their fluorescence lifetime. In this case 0 ≤ ''κ''<sup>2</sup> ≤ 4.<ref name="Demchenko2008" />
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| The FRET efficiency relates to the quantum yield and the fluorescence lifetime of the donor molecule as follows:<ref>{{cite book |first1=Irina |last1=Majoul |first2=Yiwei |last2=Jia |first3=Rainer |last3=Duden |chapter=Practical Fluorescence Resonance Energy Transfer or Molecular Nanobioscopy of Living Cells |pages=788–808 |editor-last=Pawley |editor1-first=James B. |title=Handbook Of Biological Confocal Microscopy |year=2006 |publisher=Springer |location=New York, NY |isbn=978-0-387-25921-5 |edition=3rd |doi=10.1007/978-0-387-45524-2_45}}</ref>
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| : <math> E = 1 - {\tau'_{\rm D}}/{\tau_{\rm D}} \!</math>
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| where <math>\tau'_{\rm D}</math> and <math>\tau_{\rm D}</math> are the donor fluorescence lifetimes in the presence and absence of an acceptor, respectively, or as
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| : <math> E = 1 - {F\,'_{\rm D}}/{F_{\rm D}} \!</math>
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| where <math>F\,'_{\rm D}</math> and <math>F_{\rm D}</math> are the donor fluorescence intensities with and without an acceptor, respectively.
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| ==Experimental Confirmation of the Förster resonance energy transfer theory==
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| The inverse sixth power distance dependence of Förster resonance energy transfer was experimentally confirmed by [[Lubert Stryer|Stryer]] and [[Dick Haugland|Haugland]]<ref>{{cite book |first1=Jens |last1=Michaelis |chapter=Quantitative Distance and Position Measurement using Single-Molecule FRET |pages=191–214 |editor1-first=Christoph |editor1-last=Bräuchle |editor2-first=Don Carroll |editor2-last=Lamb |editor3-first=Jens |editor3-last=Michaelis |title=Single Particle Tracking and Single Molecule Energy Transfer |publisher=Wiley-VCH |location=Weinheim |isbn=978-3-527-32296-1 |doi=10.1002/9783527628360.ch8}}</ref> using a donor and an acceptor separated on an oligoproline helix. Haugland, Yguerabide and Stryer<ref>{{cite book |editor1-last=Lakowicz |editor1-first=Joseph R.|title=Principles|year=1991|publisher=Plenum Press|location=New York |isbn=978-0-306-43875-2|page=172}}</ref> also experimentally demonstrated the theoretical dependence of Förster resonance energy transfer on the overlap integral by using a fused indolosteroid as a donor and a ketone as an acceptor.
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| ==Methods to measure FRET efficiency==
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| In fluorescence [[microscopy]], fluorescence [[confocal laser scanning microscopy]], as well as in [[molecular biology]], FRET is a useful tool to quantify molecular dynamics in [[biophysics]] and [[biochemistry]], such as [[protein]]-protein interactions, protein–[[DNA]] interactions, and protein conformational changes. For monitoring the complex formation between two molecules, one of them is labeled with a donor and the other with an acceptor. The FRET efficiency is measured and used to identify interactions between the labeled complexes. There are several ways of measuring the FRET efficiency by monitoring changes in the fluorescence emitted by the donor or the acceptor.<ref>{{cite web|title=Fluorescence Resonance Energy Transfer Protocol|url=http://coil.bio.ed.ac.uk/Protocols/FRET.htm|publisher=Wellcome Trust|accessdate=24 June 2012}}</ref>
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| ===Sensitized emission=== | |
| One method of measuring FRET efficiency is to measure the variation in acceptor emission intensity.<ref name=Clegg2009p1-57/> When the donor and acceptor are in proximity (1–10 nm) due to the interaction of the two molecules, the acceptor emission will increase because of the [[intermolecular]] FRET from the donor to the acceptor. For monitoring protein conformational changes, the target protein is labeled with a donor and an acceptor at two loci. When a twist or bend of the protein brings the change in the distance or relative orientation of the donor and acceptor, FRET change is observed. If a molecular interaction or a protein conformational change is dependent on [[ligand]] binding, this FRET technique is applicable to fluorescent indicators for the ligand detection.
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| ===Photobleaching FRET===
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| FRET efficiencies can also be inferred from the [[photobleaching]] rates of the donor in the presence and absence of an acceptor.<ref name=Clegg2009p1-57/> This method can be performed on most fluorescence microscopes; one simply shines the excitation light (of a frequency that will excite the donor but not the acceptor significantly) on specimens with and without the acceptor fluorophore and monitors the donor fluorescence (typically separated from acceptor fluorescence using a bandpass filter) over time. The timescale is that of photobleaching, which is seconds to minutes, with fluorescence in each curve being given by
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| <math>(\mbox{background})+(\mbox{constant})*e^{-(\mbox{time})/{\tau_{\rm pb}}}</math>
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| where <math>{\tau_{\rm pb}}</math> is the photobleaching decay time constant and depends on whether the acceptor is present or not. Since photobleaching consists in the permanent inactivation of excited fluorophores, resonance energy transfer from an excited donor to an acceptor fluorophore prevents the photobleaching of that donor fluorophore, and thus high FRET efficiency leads to a longer photobleaching decay time constant:
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| <math> E = 1 - {\tau_{\rm pb}}/{\tau'_{\rm pb}} \!</math>
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| where <math>{\tau'_{\rm pb}}</math> and <math>{\tau_{\rm pb}}</math> are the photobleaching decay time constants of the donor in the presence and in the absence of the acceptor, respectively.
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| (Notice that the fraction is the reciprocal of that used for lifetime measurements).
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| This technique was introduced by Jovin in 1989.<ref>{{cite book |first1=János |last1=Szöllősi |first2=Denis R. |last2=Alexander |chapter=The Application of Fluorescence Resonance Energy Transfer to the Investigation of Phosphatases |pages=203–24 |editor1-first=Susanne |editor1-last=Klumpp |editor2-first=Josef |editor2-last=Krieglstein |title=Protein Phosphatases |series=Methods in Enzymology, Volume 366 |year=2007 |publisher=Elsevier |location=Amsterdam |isbn=978-0-12-182269-9 |doi=10.1016/S0076-6879(03)66017-9}}</ref> Its use of an entire curve of points to extract the time constants can give it accuracy advantages over the other methods. Also, the fact that time measurements are over seconds rather than nanoseconds makes it easier than fluorescence lifetime measurements, and because photobleaching decay rates do not generally depend on donor concentration (unless acceptor saturation is an issue), the careful control of concentrations needed for intensity measurements is not needed. It is, however, important to keep the illumination the same for the with- and without-acceptor measurements, as photobleaching increases markedly with more intense incident light.
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| ===Lifetime measurements===
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| FRET efficiency can also be determined from the change in the fluorescence [[Fluorescence#Lifetime|lifetime]] of the donor.<ref name=Clegg2009p1-57/> The lifetime of the donor will decrease in the presence of the acceptor. Lifetime measurements of FRET are used in [[Fluorescence-lifetime imaging microscopy]].
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| ==Fluorophores used for FRET==
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| [[File:Proteolytic cleavage of a Dual-GFP fusion FRET-pair.png|thumb|If the linker is intact, excitation at the absorbance wavelength of CFP (414nm) causes emission by YFP (525nm) due to FRET. If the linker is cleaved by a protease, FRET is abolished and emission is at the CFP wavelength (475nm).]]
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| ===CFP-YFP pairs===
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| One common pair fluorophores for biological use is a [[cyan fluorescent protein]] ('''CFP''') – [[yellow fluorescent protein]] ('''YFP''') pair.<ref>{{cite journal|last=Periasamy|first=Ammasi|title=Fluorescence resonance energy transfer microscopy: a mini review|journal=Journal of Biomedical Optics|date=July 2001|volume=6|issue=3|pages=287–291|doi=10.1117/1.1383063|pmid=11516318|bibcode = 2001JBO.....6..287P }}</ref> Both are color variants of [[green fluorescent protein]] ('''GFP'''). Labeling with organic fluorescent dyes requires purification, chemical modification, and intracellular injection of a host protein. GFP variants can be attached to a host protein by [[genetic engineering]] which can be more convenient. Additionally, a fusion of CFP and YFP linked by a [[protease]] cleavage sequence can be used as a cleavage assay.<ref>{{cite journal|last=Nguyen|first=AW|coauthors=Daugherty, PS|title=Evolutionary optimization of fluorescent proteins for intracellular FRET.|journal=Nature biotechnology|date=March 2005|volume=23|issue=3|pages=355–60|pmid=15696158}}</ref>
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| ===BRET===
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| A limitation of FRET is the requirement for external illumination to initiate the fluorescence transfer, which can lead to background noise in the results from direct excitation of the acceptor or to [[photobleaching]]. To avoid this drawback, [[Bioluminescence]] Resonance Energy Transfer (or '''BRET''') has been developed.<ref>{{cite book |first1=Nicola |last1=Bevan |first2=Stephen |last2=Rees |chapter=Pharmaceutical Applications of GFP and RCFP |chapterurl=http://books.google.com/books?id=v8Y4zrEofpIC&pg=PA361 |pages=361–90 |editor1-first=Martin |editor1-last=Chalfie |editor2-first=Steven R. |editor2-last=Kain |series=Methods of Biochemical Analysis, Volume 47 |title=Green Fluorescent Protein: Properties, Applications and Protocols |year=2006 |publisher=John Wiley & Sons |location=Hoboken, NJ |isbn=978-0-471-73682-0 |edition=2nd |doi=10.1002/0471739499.ch16}}</ref> This technique uses a bioluminescent [[luciferase]] (typically the luciferase from ''[[Renilla reniformis]]'') rather than CFP to produce an initial photon emission compatible with YFP.
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| ===Homo-FRET===
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| In general, "FRET" refers to situations where the donor and acceptor proteins (or "fluorophores") are of two different types. In many biological situations, however, researchers might need to examine the interactions between two, or more, proteins of the same type—or indeed the same protein with itself, for example if the protein folds or forms part of a polymer chain of proteins<ref>{{cite journal |doi=10.1016/S0006-3495(01)76265-0 |title=Homo-FRET Microscopy in Living Cells to Measure Monomer-Dimer Transition of GFP-Tagged Proteins |year=2001 |last1=Gautier |first1=I. |last2=Tramier |first2=M. |last3=Durieux |first3=C. |last4=Coppey |first4=J. |last5=Pansu |first5=R.B. |last6=Nicolas |first6=J.-C. |last7=Kemnitz |first7=K. |last8=Coppey-Moisan |first8=M. |journal=Biophysical Journal |volume=80 |issue=6 |pages=3000–8 |pmid=11371472 |pmc=1301483|bibcode = 2001BpJ....80.3000G }}</ref> or for other questions of quantification in biological cells.<ref>{{cite journal |doi=10.1016/j.bpj.2009.07.059 |title=Homo-FRET Imaging Enables Quantification of Protein Cluster Sizes with Subcellular Resolution |year=2009 |last1=Bader |first1=Arjen N. |last2=Hofman |first2=Erik G. |last3=Voortman |first3=Jarno |last4=Van Bergen En Henegouwen |first4=Paul M.P. |last5=Gerritsen |first5=Hans C. |journal=Biophysical Journal |volume=97 |issue=9 |pages=2613–22 |pmid=19883605 |pmc=2770629|bibcode = 2009BpJ....97.2613B }}</ref>
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| Obviously, spectral differences will not be the tool used to detect and measure FRET, as both the acceptor and donor protein emit light with the same wavelengths. Yet researchers can detect differences in the polarisation between the light which excites the fluorophores and the light which is emitted, in a technique called FRET anisotropy imaging; the level of quantified anisotropy (difference in polarisation between the excitation and emission beams) then becomes an indicative guide to how many FRET events have happened.<ref>{{cite journal |doi=10.1039/b920242k |title=Fluorescence anisotropy: From single molecules to live cells |year=2010 |last1=Gradinaru |first1=Claudiu C. |last2=Marushchak |first2=Denys O. |last3=Samim |first3=Masood |last4=Krull |first4=Ulrich J. |journal=The Analyst |volume=135 |issue=3 |pages=452–9 |pmid=20174695|bibcode = 2010Ana...135..452G }}</ref>
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| ==Applications==
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| FRET has been used to measure distance and detect molecular interactions in a number of systems and has applications in biology and chemistry.<ref>{{cite book|last=Lakowicz|first=Joseph R.|title=Principles of fluorescence spectroscopy|year=1999|publisher=Kluwer Acad./Plenum Publ.|location=New York, NY |isbn=978-0-306-46093-7|pages=374–443|edition=2nd}}</ref> FRET can be used to measure distances between domains a single protein and therefore to provide information about protein conformation.<ref>{{cite journal |doi=10.1016/S0959-440X(00)00249-9 |title=The use of FRET imaging microscopy to detect protein–protein interactions and protein conformational changes in vivo |year=2001 |last1=Truong |first1=Kevin |last2=Ikura |first2=Mitsuhiko |journal=Current Opinion in Structural Biology |volume=11 |issue=5 |pages=573–8 |pmid=11785758}}</ref> FRET can also detect interaction between proteins.<ref>{{cite journal |doi=10.1016/S0962-8924(98)01434-2 |title=Using GFP in FRET-based applications |year=1999 |last1=Pollok |first1=B |journal=Trends in Cell Biology |volume=9 |issue=2 |pages=57–60 |pmid=10087619 |last2=Heim |first2=R}}</ref> Applied in vivo in living cells, FRET has been used to detect the location and interactions of genes and cellular structures including intergrins and membrane proteins.<ref>{{cite journal |doi=10.1083/jcb.200210140 |title=Fluorescence resonance energy transfer (FRET) microscopy imaging of live cell protein localizations |year=2003 |last1=Sekar |first1=R. B. |journal=The Journal of Cell Biology |volume=160 |issue=5 |pages=629–33 |pmid=12615908 |last2=Periasamy |first2=A |pmc=2173363}}</ref> FRET can be used to obtain information about metabolic or signaling pathways.<ref>{{cite book |first1=Qiang |last1=Ni |first2=Jin |last2=Zhang |chapter=Dynamic Visualization of Cellular Signaling |chapterurl=http://books.google.com/books?id=qrGsL_wYdHMC&pg=PA79 |pages=79–97 |year=2010 |editor1-last=Endo |editor1-first=Isao |editor2-first=Teruyuki |editor2-last=Nagamune |title=Nano/Micro Biotechnology |publisher=Springer |isbn=978-3-642-14946-7 |series=Advances in Biochemical Engineering/Biotechnology, Volume 119 |doi=10.1007/10_2008_48 |bibcode=2010nmb..book...79N |pmid=19499207}}</ref> FRET is also used to study [[lipid rafts]] in [[cell membranes]].<ref>{{cite journal |doi=10.1080/09687860500473002 |title=Fluorescence-quenching and resonance energy transfer studies of lipid microdomains in model and biological membranes (Review) |year=2006 |last1=Silvius |first1=John R. |last2=Nabi |first2=Ivan Robert |journal=Molecular Membrane Biology |volume=23 |pages=5–16 |pmid=16611577 |issue=1}}</ref>
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| FRET and BRET are also the common tools in the study of [[Enzyme kinetics|biochemical reaction kinetics]] and [[molecular motors]].
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| ==Other methods==
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| A different, but related, mechanism is [[Dexter Electron Transfer]].
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| An alternative method to detecting protein–protein proximity is the [[bimolecular fluorescence complementation]] (BiFC) where two halves of a YFP are fused to a protein. When these two halves meet they form a fluorophore after about 60 s – 1 hr.<ref name="pmid11983170">{{cite journal |doi=10.1016/S1097-2765(02)00496-3 |title=Visualization of Interactions among bZIP and Rel Family Proteins in Living Cells Using Bimolecular Fluorescence Complementation |year=2002 |last1=Hu |first1=Chang-Deng |last2=Chinenov |first2=Yurii |last3=Kerppola |first3=Tom K. |journal=Molecular Cell |volume=9 |issue=4 |pages=789–98 |pmid=11983170}}</ref>
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| ==See also==
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| *[[Förster coupling]]
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| ==References==
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| {{reflist}}
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| ==External links==
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| *{{YouTube|id=3bmb_oDl6ws|title=FRET effect in a thin film}}
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| {{DEFAULTSORT:Forster Resonance Energy Transfer}}
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| [[Category:Imaging]]
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| [[Category:Fluorescence]]
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| [[Category:Biochemistry methods]]
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| [[Category:Biophysics]]
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| [[Category:Cell imaging]]
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| [[Category:Optical phenomena]]
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| [[Category:Protein–protein interaction assays]]
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| [[Category:Fluorescence techniques]]
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| [[Category:Cell biology]]
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| [[Category:Laboratory techniques]]
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| [[Category:Molecular biology techniques]]
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