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I need help with the reaction between fluorescein and blood in the method of detecting latent blood stains.

I find it hard to find any literature on this subject. As far as I am concerned, the fluorescein is reduced into fluorescin in a stock solution with powdered zinc, distilled water and sodium hydroxide pellets. $\ce{Fe^2+}$ (found in the latent blood) is oxidized into $\ce{Fe^3+}$ with hydrogen peroxide. When fluorescin is reacting with iron ions in the haemoglobin, it will be oxidized back to fluorescein.

Can anyone help me with this? Maybe even on a molecular level.

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Fluorescin(left), a non-fluorescent compound, reacts with iron in residual blood samples to produce highly fluorescent fluorescein(right).

Fluorescin and Fluorescein

The reference$\ce{^{[2]}}$ from which the following excerpt is taken describes the chemistry, preparation of reagents, and application to forensics.

Fluorescin is the oxidized colorless form of fluorescein. Fluorescin reduced with hydrogen peroxide is immediately oxidized to fluorescein in the presence of blood-associated proteins and iron ion found in hemoglobin. Fluorescein fluoresces when viewed using blue light and orange or yellow filters, whereas fluorescin will not fluoresce under the same lighting conditions.

Literature Resource

An excellent starting point to consider for searching for relevant literature is PubMed.

References

  1. Image sources - PubChem
  2. Google Books - Complete Crime Scene Investigation Handbook, Everett Baxter, Jr.
  3. Latent-Prints.com - Fluorescein Detection of Latent Bloodstains
  4. The Presumptive Reagent Fluorescein for Detection of Dilute Bloodstains and Subsequent STR Typing of Recovered DNA
  5. A Comparison of the Bluestar and Luminol Effectiveness in Bloodstain Detection
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