Coomassie Blue (also called Coomassie Brilliant Blue) is a protein stain derived from triphenylmethane dye. It takes its name from the brilliant blue hue it imparts. Within latent print examination, the key characteristic of Coomassie Blue is its ability to bind strongly to the proteins present in blood. This makes it specifically valuable when attempting to develop and visualize latent prints contaminated with blood.
Equipment
- Fume hood (strongly recommended): Coomassie Blue involves volatile solvents like methanol.
- Graduated cylinder: For accurate measurement of liquids.
- Large glass beaker or container: For mixing the solution.
- Magnetic stir bar and stir plate (optional): For consistent, efficient mixing.
- Spray bottle: For application on smaller items or surfaces.
- Shallow trays or containers: For submersion of larger items.
- Personal Protective Equipment (PPE): Gloves, lab coat, eye protection, and a suitable mask or respirator.
Ingredients and Quantities for a 1-Liter Solution of Coomassie Blue
- Coomassie Brilliant Blue R-250 dye: 0.44 g
- Methanol: 200 mL
- Glacial Acetic Acid: 40 mL
- Purified or Distilled Water: 200 mL (adjust this and the methanol amount to reach a final volume of 1 liter)
Mixing Procedure
- Safety First: Work in a fume hood due to the fumes. Don your PPE.
- Combine: In the glass beaker, add the Coomassie Brilliant Blue dye to the methanol.
- Stir: Use a stir bar and plate or stir vigorously by hand until the dye fully dissolves.
- Add Acid: Slowly pour in the glacial acetic acid while continuing to stir.
- Dilute: Gradually add purified water while stirring, bringing the final volume to 1 liter.
- Transfer: Pour the prepared Coomassie Blue solution into either a spray bottle for localized use or a storage container for later use. Label clearly with contents and date.
Latent Print Processing Using Coomassie Blue
- Surface Assessment: Coomassie Blue is primarily used on porous and non-porous surfaces. It's particularly well-suited to enhancing faint, diluted, or aged bloodstains.
- Pretreatment: Ensure other fingerprint development techniques have been exhausted before using Coomassie Blue, as it reacts with proteins and might interfere with subsequent processes.
- Application:
- Spray: For localized application, lightly mist the target area.
- Submersion: For larger items, place them in a shallow tray and pour Coomassie Blue until the prints are covered. Allow sufficient time for the reaction.
- Rinsing: Gently rinse the surface with distilled water to remove excess dye and improve contrast.
- Visualization: Bloody prints will turn a vibrant blue or bluish-purple color.
- Documentation: Take high-quality photographs of the developed latent prints before the color begins to fade.
Storage and Shelf Life
- Container: Store Coomassie Blue in a tightly sealed, dark glass or opaque container to prevent light and solvent evaporation.
- Conditions: Store in a cool, dark environment away from heat and light.
- Shelf Life: Properly mixed and stored Coomassie Blue generally has a shelf life of about one year. Check for signs of precipitation or degradation before use.
Important Notes:
- Coomassie Blue is a destructive technique. Always document the area thoroughly prior to its use.
- This reagent is considered relatively safe, but always consult its Safety Data Sheet (SDS) for proper handling precautions.