D.A.B., or 3,3'-Diaminobenzidine tetrahydrochloride, is a highly sensitive blood reagent used to visualize latent prints composed of trace amounts of blood. The beauty of D.A.B. is its ability to react with the peroxidase-like activity found in hemoglobin (a component of blood). This reaction creates a brown, insoluble product— making blood prints clearly visible on both porous and non-porous surfaces.
Equipment
- Fume hood (Highly Recommended)
- Glassware: Beakers, stirring rod, graduated cylinder
- Chemicals (See ingredients below)
- Distilled or deionized water
- Spray bottle or tray for application
- Gloves, lab coat, and eye protection
- Camera for photographing results
Ingredients for a 1-Liter D.A.B. Solution
- 3,3'-Diaminobenzidine tetrahydrochloride (DAB): 0.5 grams
- Sodium Citrate Buffer (pH 4-6): Pre-made, but can be formulated if needed.
- Hydrogen Peroxide (30%): 20 mL
- Distilled or deionized water: Approximately 1 Liter
D.A.B. Mixing Procedure
- Safety First: Work in a fume hood due to the potential release of irritating fumes with the use of hydrogen peroxide. Wear gloves, a lab coat, and eye protection.
- Prepare Buffer: Add enough sodium citrate buffer (pH 4-6) to a clean beaker to make up the majority of your 1-Liter solution (e.g., about 900 ml).
- Dissolve D.A.B.: Carefully add the 0.5 grams of D.A.B. to the buffer and stir gently to dissolve.
- Add Hydrogen Peroxide: Slowly add the 20 mL of hydrogen peroxide while stirring.
- Top Up: Bring the solution up to the 1-Liter mark with distilled or deionized water.
Latent Print Processing with D.A.B.
- Visual Examination: Start with a thorough examination of the item using white light and possible oblique lighting techniques.
- Forensic Light Source: Examine the item with alternative light sources (ALS) if available, as blood can have some inherent fluorescence.
- D.A.B. Application:
- Spraying: For larger surfaces or more control, carefully spray the item with the D.A.B. solution.
- Submersion: Smaller items can be submerged in a tray containing D.A.B.
- Reaction Time: Allow the D.A.B. to react. Brown deposits indicating blood should appear within a few minutes.
- Rinse: Once development is sufficient, gently rinse the item with distilled water to stop the reaction.
- Photography: Document the developed prints immediately for best contrast as they may fade over time.
Storing D.A.B.
- Light-Sensitive: Store the D.A.B. solution in a dark, amber-colored bottle.
- Refrigeration: Keep the solution refrigerated.
- Caution: DAB is a potential carcinogen, so handle it with appropriate precautions.
D.A.B. Shelf Life
The shelf life of a mixed D.A.B. solution is limited. It is best used within 48 hours when stored correctly.
Important Considerations
- D.A.B. can be a messy reagent, so take precautions to avoid staining work areas and clothing.
- Always perform a positive and negative control test with your D.A.B. solution for quality control.
- D.A.B. is highly sensitive but may give false positives with some metals or vegetable materials.