DFO

DFO (1,8-Diazafluoren-9-one) is a highly sensitive chemical reagent mainly used to develop latent fingerprints on porous surfaces like paper, cardboard, and untreated wood.
It reacts with the amino acids present in fingerprint residue.
DFO is a ninhydrin analog, meaning it has a similar chemical structure but offers advantages in terms of fluorescence.

Advantages of DFO

Fluorescence: Prints developed with DFO fluoresce a bright yellow-orange when excited by a blue-green light source (around 530nm). This is great for multicolored or patterned backgrounds where ninhydrin visualization can be difficult.
Sensitivity: Studies have suggested that DFO can develop up to 2.5 times as many latent prints as ninhydrin.
Bloodstain Development: DFO can also sometimes develop weak bloodstains.

Fume Hood: It's highly recommended due to solvent fumes.
Spray Bottle (Solvent Resistant): For spraying DFO solution.
Dipping Tray: For dipping items into DFO solution.
Drying Rack/Chamber: With controlled airflow for drying processed evidence.
Forensic Light Source: With excitation around 530nm (blue-green)
Orange Filter: For your camera or viewing goggles.
Personal Protective Equipment: Lab coat, gloves, safety glasses/goggles, respirator if needed.

Here's a common DFO formulation using HFE-7100 solvent :

Safety First: Work in a fume hood. Wear full personal protective equipment.
Dissolve DFO: In a clean glass container, dissolve the DFO powder in the methanol. Swirl until completely dissolved.
Add Solvent: Slowly add petroleum ether or HFE-7100 while stirring until you reach the total volume of 1 liter.
Label and Store: Transfer to an appropriate, labeled container, ensuring it's tightly sealed.

Pretreatment: Assess the item and consider any pretreatments if needed (magnetic powder, etc.).
Application:

Drying: Air-dry the item in a well-ventilated drying chamber/rack.
Heat (Optional): Development can be accelerated with controlled humidity and heat (e.g., oven at around 100°C for 10-20 minutes).
Visualization: Excite the treated item with a blue-green light source and view the developed prints through an orange filter.
Documentation: Photograph prints with the orange filter before any further processing.

Light Sensitive: Store DFO solution in an amber bottle to protect it from light degradation.
Cool Location: Store the solution in a cool, dark place. Refrigeration is often recommended.
Tightly Sealed: Ensure the container is airtight to prevent solvent evaporation.

Shelf life depends on storage conditions and the specific solvent used.
With proper storage, DFO solutions can remain effective for several months, sometimes even a year.
Regularly test your solution with a known fingerprint standard to gauge its potency.