Fluorescein

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Fluorescein

Fluorescein
Systematic name	Fluorescein
Chemical formula	C₂₀H₁₂O₅
Molecular mass	332.32 g/mol
Density	x.xxx g/cm³
Melting point	xx.x °C
Boiling point	xx.x °C
CAS number	^*
SMILES	OC(C1=C(C(C(C=CC(O)=C3)=C3O2)=C4C2=CC(C=C4)=O)C=CC=C1)=O
Chemical infobox

Fluorescein Isothiocyanate
Systematic name	Fluorescein Isothiocyanate
Chemical formula	C_xH_xN_xO_x
Molecular mass	xx.xx g/mol
Density	x.xxx g/cm³
Melting point	xx.x °C
Boiling point	xx.x °C
CAS number	^*
SMILES	xxxxx
Chemical infobox

Fluorescein is a fluorophore commonly used in microscopy, in a type of dye laser as the gain medium, and in forensics and serology to detect latent blood stains. Fluorescein has an absorption maximum at 490 nm and emission maximum of 514 nm (in water). Also, fluorescein has an isoabsorptive point (equal absorption for all pH values) at 460 nm.

Chemical Properties

The fluorescence of this molecule is very high, and excitation occurs at 494 nm and emission at 525 nm. The isothiocyanate group (-N=C=S) replaces a hydrogen atom on the bottom ring of the structure, and is reactive with amine groups on proteins inside cells. Fluorescein isothiocyanate is often abbreviated as FITC.

Fluorescein has a pK_a at 6.4 and multiple ionization equilibria. This leads to pH dependent absorption and emission over the range of 5 to 9. Also, the fluorescence lifetimes of the protonated and deprotonated forms of fluorescein are approximately 3 and 4 ns, which allows for pH determination from non-intensity based measurements. The lifetimes can be recovered using time-correlated single photon counting or phase-modulation fluorimetry.

There are many other fluorescein derivatives, such as Oregon Green, Tokyo Green, SNAFL, and carboxynapthofluorescein. These have been tailored for various chemical and biological applications where higher photostability, different spectral characteristics, or different attachment groups are needed.

Synthesis

Fluorescein can be prepared from phthalic anhydride and resorcinol in the presence of zinc chloride. (Oxygen missing fluorescein product in figure)

Applications

Uses in River Systems

One of its more recognizable uses is in the Chicago River, where fluorescein is used to dye the river green on St. Patrick's Day.

Other uses of fluorescein include using it as a water-soluble dye added to rainwater in environmental testing simulations to aid in locating and analyzing any water leaks, and in Australia and New Zealand as a methylated spirit dye.

Biological Research

In biology, the isothiocyanate derivative of fluorescein is often used to label and track cells in fluorescence microscopy applications. Additional biologically active molecules (such as antibodies) may also be attached to fluorescein, allowing biologists to target the fluorophore to specific proteins or structures within cells. This application is common in yeast display.

Ophthalmic (Eye) Applications

Fluorescein sodium is used extensively as a diagnostic tool in the field of ophthalmology. It is applied topically in the form of a drop or it can be injected intravenously to produce a fluorescein angiogram.

Topical fluorescein is useful in the diagnosis of corneal abrasions, corneal ulcers, herpetic corneal infections, and dry eye. Fluorescein angiography is used to diagnose and categorize age-related macular degeneration, diabetic retinopathy, inflammatory intraocular conditions, and intraocular tumors.

External links

Fluorone dyes | Staining dyes | Fluorescent dyes

Fluorescein | Fluorescein