fluo·​res·​ce·​in | \ flu̇-ˈre-sē-ən How to pronounce fluorescein (audio) , flȯ- \

Definition of fluorescein

: a yellow or red crystalline dye C20H12O5 with a bright yellow-green fluorescence in alkaline solution

Examples of fluorescein in a Sentence

Recent Examples on the Web Researchers dumped a dye, fluorescein, into the wells and monitored the marine waters along the beaches. Warren Cornwall, Science | AAAS, 23 Apr. 2020 The polyacrylate was then bathed in molecules of fluorescein, an orange dye with a yellow-green fluorescence that's commonly used as a scientific marker. David Grossman, Popular Mechanics, 18 Dec. 2018 With the fluorescein in place, scientists then add an acid that hinders the negative charges in the polyacrylate gel. David Grossman, Popular Mechanics, 18 Dec. 2018 Our doctor placed yellow drops containing fluorescein sodium in his eye. Dan Olson, WIRED, 29 Sep. 2008

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'fluorescein.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of fluorescein

1871, in the meaning defined above

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Time Traveler for fluorescein

Time Traveler

The first known use of fluorescein was in 1871

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Dictionary Entries Near fluorescein



fluorescein sodium

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Cite this Entry

“Fluorescein.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/fluorescein. Accessed 22 Oct. 2021.

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More Definitions for fluorescein


flu·​o·​res·​ce·​in | \ -ˈes-ē-ən How to pronounce fluorescein (audio) \

Medical Definition of fluorescein

: a yellow or red crystalline dye C20H12O5 with a bright yellow-green fluorescence in alkaline solution that is used as the sodium salt as an aid in diagnosis (as of lesions and foreign bodies in the cornea or of brain tumors)

More from Merriam-Webster on fluorescein

Britannica.com: Encyclopedia article about fluorescein


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