Editing Lanthanide (section)

===Life science===
Lanthanide complexes can be used for optical imaging. Applications are limited by the [[lability]] of the complexes.<ref>{{cite book |first1=Thomas Just |last1=Sørenson|first2=Stephen |last2=Faulkner|title=Metal Ions in Bio-Imaging Techniques|publisher=Springer|year=2021|pages=137–156 |chapter=Chapter 5. Lanthanide Complexes Used for Optical Imaging |doi=10.1515/9783110685701-011|s2cid=233653968}}</ref> 

Some applications depend on the unique luminescence properties of lanthanide [[chelates]] or [[cryptate]]s.<ref>Daumann, Lena J.; Op den Camp, Huub J.M.; "The Biochemistry of Rare Earth Elements" pp 299-324 in "Metals, Microbes and Minerals: The Biogeochemical Side of Life" (2021) pp xiv + 341. Walter de Gruyter, Berlin. Editors Kroneck, Peter M.H. and Sosa Torres, Martha. [https://www.de Gruyter.com/document/doi/10.1515/9783110589771-010 DOI 10.1515/9783110589771-010] {{Webarchive|url=https://web.archive.org/web/20220908150824/https://www2022.de/ |date=8 September 2022 }}</ref><ref>{{cite journal|last1=Bunzil|first1=Jean-Claude|first2=Claude|last2=Piguet|title=Taking advantage of luminescent lanthanide ions|journal=Chemical Society Reviews|date=September 2005|doi=10.1039/b406082m|url=http://lib.semi.ac.cn:8080/tsh/dzzy/wsqk/selected%20papers/Chemical%20Society%20Reviews/34-1048.pdf|access-date=22 December 2012|volume=34|issue=12|pages=1048–77|pmid=16284671|archive-url=https://web.archive.org/web/20130118024445/http://lib.semi.ac.cn:8080/tsh/dzzy/wsqk/selected%20papers/Chemical%20Society%20Reviews/34-1048.pdf|archive-date=18 January 2013|url-status=dead}}</ref> These are well-suited for this application due to their large [[Fluorescence|Stokes shifts]] and extremely long emission lifetimes (from [[microsecond]]s to [[millisecond]]s) compared to more traditional fluorophores (e.g., [[fluorescein]], [[allophycocyanin]], [[phycoerythrin]], and [[rhodamine]]). 

The biological fluids or serum commonly used in these research applications contain many compounds and proteins which are naturally fluorescent. Therefore, the use of conventional, steady-state fluorescence measurement presents serious limitations in assay sensitivity. Long-lived fluorophores, such as lanthanides, combined with time-resolved detection (a delay between excitation and emission detection) minimizes prompt fluorescence interference.

[[Time-resolved spectroscopy|Time-resolved fluorometry (TRF)]] combined with [[Förster resonance energy transfer|Förster resonance energy transfer (FRET)]] offers a powerful tool for drug discovery researchers: Time-Resolved Förster Resonance Energy Transfer or TR-FRET. TR-FRET combines the low background aspect of TRF with the homogeneous assay format of FRET. The resulting assay provides an increase in flexibility, reliability and sensitivity in addition to higher throughput and fewer false positive/false negative results.

This method involves two fluorophores: a donor and an acceptor. Excitation of the donor fluorophore (in this case, the lanthanide ion complex) by an energy source (e.g. flash lamp or laser) produces an energy transfer to the acceptor fluorophore if they are within a given proximity to each other (known as the [[Förster resonance energy transfer|Förster's radius]]). The acceptor fluorophore in turn emits light at its characteristic wavelength.

The two most commonly used lanthanides in life science assays are shown below along with their corresponding acceptor dye as well as their excitation and emission wavelengths and resultant [[Stokes shift]] (separation of excitation and emission wavelengths).
{| class="wikitable" |align="center" |+ Life Science lanthanide Donor-Acceptor pairings
!Donor
!Excitation⇒Emission λ (nm)
!Acceptor
!Excitation⇒Emission λ (nm)
!Stokes Shift (nm)
|-
|Eu<sup>3+</sup>
|340⇒615
|[[Allophycocyanin]]
|615⇒660
|320
|-
|Tb<sup>3+</sup>
|340⇒545
|[[Phycoerythrin]]
|545⇒575

|235
|}