Fluorescein (FITC)

General Information (from wikipedia)

Species Molecular Weight (g/mol) Density (g/L) Radius (m) Reference
Fluorescein 332.306 D R [1]
Fluprescein Sodium Salt 376.27 D R [3], [4]

Fluorescein is a fluorophore commonly used in microscopy, in a type of dye laser as the gain medium, in forensics and serology to detect latent blood stains, and in dye tracing. Fluorescein has an absorption maximum at 494 nm and emission maximum of 521 nm (in water). Also, fluorescein has an isosbestic point (equal absorption for all pH values) at 460 nm. Fluorescein is also known as a color additive (D&C Yellow no. 7). The disodium salt form of fluorescein is known as D&C Yellow no. 8.

The fluorescence of this molecule is very high, and excitation occurs at 494 nm and emission at 521.

Fluorescein has a pKa of 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.

Diffusion of FITC in water:

  • Alone: $D~=0.64 \times 10^{-9}\ m^{2}/s$ [2]
  • Alone: $D~= 0.49 \times 10^{-9}\ m^{2}/s$ [3]

Diffusion of FITC in PBS:

  • Alone: $D~=2.7 \times 10^{-10}\ m^{2}/s$ [1]
  • FITC-dextran, 70 kD: $D~=2.3 \times 10^{-11}\ m^{2}/s$ [1]

Diffusion of FITC in a 70000 MW dextran solution

  • Alone in 4 gm/dl soution: $D~=0.49 \times 10^{-9}\ m^{2}/s$ [2]
  • Alone in 8 gm/dl soution: $D~=0.38 \times 10^{-9}\ m^{2}/s$ [2]

Diffusion of FITC in cellular matrix:

  • Alone in bioflim cell clusters: $D~= 0.16 \times 10^{-9}\ m^{2}/s$ [3]
  • Alone in osteocytic pericellular matrix: $D~=0.3 \pm 0.05 \ 10^{-9}\ m^{2}/s$ [4]
1. Biophys J. 1998 July; 75(1): 557–567
2. Galambos, P. and F.K. Forster. Micro-Fluidic Diffusion Coefficient Measurement. in Micro Total Analysis Systems. 1998.
3. Rani, S.A., B. Pitts, and P.S. Stewart, Rapid Diffusion of Fluorescent Tracers into Staphylococcus epidermidis Biofilms Visualized by Time Lapse Microscopy. Antimicrob. Agents Chemother., 2005. 49(2): p. 728-732
4. Wang, L., et al., In situ measurement of solute transport in the bone lacunar-canalicular system. PNAS, 2005. 102(33): p. 11911-11916.
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