Acid Yellow 7 is a fluorescent dye widely used to enhance blood-containing latent fingerprints and footwear impressions. This reagent has a unique affinity for proteins found in blood, causing the blood residue to become a contrasting yellow color. Moreover, Acid Yellow 7 fluoresces a brilliant yellow-green when observed under blue or blue-green light sources, enhancing the visibility and ease of documentation of these prints.
Equipment
- Fume Hood: Processing with Acid Yellow 7 typically takes place in a fume hood due to the presence of acetic acid vapors.
- Spray Bottle: A fine-mist spray bottle ensures even application of the reagent to the area of interest.
- Alternate Light Source (ALS): An ALS with wavelengths in the blue/blue-green region (450-500nm) is needed to visualize the fluorescence.
- Orange Filter: An orange barrier filter fitted to your camera or your goggles will improve the contrast of the developed prints during photography.
Materials and Chemicals for 1 Liter
- Acid Yellow 7 Dye: Approximately 0.5 to 1 grams
- Distilled Water: 900 mL
- Acetic Acid (Glacial): 80 mL
- Ethanol (95%): 20 mL
Mixing Procedures
- Preparation: Work within a fume hood and wear appropriate personal protective equipment (gloves, lab coat, eye protection).
- Dissolve Dye: Slowly dissolve the Acid Yellow 7 dye into the distilled water. You can use gentle stirring with a clean glass stir rod to aid the process.
- Add Solvents: Carefully add the acetic acid and then the ethanol to the dye solution. Note: Acetic acid has strong vapors – proceed with caution.
- Mix Thoroughly: Stir the solution gently until a homogeneous mixture is achieved.
- Labeling: Transfer the finished Acid Yellow 7 solution to a properly labeled chemical storage bottle. Indicate the preparation date, any relevant hazards, and your initials.
Processing Procedure
- Fixation (Optional): If not previously treated, consider using a 2% sulfosalicylic acid fixative solution on the blood prints before applying Acid Yellow 7. This helps prevent dissolving or washing away of the prints during the staining process
- Application: Lightly mist the Acid Yellow 7 solution over the area where potential blood-contaminated prints may be present. Excess reagent can obscure detail, so a light, even application is important.
- Visualization: Allow a brief development time (seconds to minutes). After, examine the area with a blue to blue-green ALS and an orange filter for visualization of the fluorescing prints.
- Documentation: Photograph the fluorescing prints with the ALS and orange filter for appropriate documentation.
Proper Storage
- Storage Container: Store Acid Yellow 7 in an amber glass bottle to protect the reagent from light degradation.
- Environment: Keep the storage location cool and away from direct sunlight or heat sources.
- Labeling: Ensure the bottle is properly labeled with the chemical name, concentration, date of preparation, and relevant safety warnings.
Shelf Life
Acid Yellow 7 has a reasonably long shelf life with proper storage. It can generally be used for up to 6 months to a year. However, regularly inspecting the reagent for clarity and checking for any precipitation or other inconsistencies is essential.