Fluorescence/Chemical Development Flashcards
How do lasers differ from the light of torch?
lasers have a low divergence and the other property is that it is monochromatic therefore the light is coherent.
What is the most useful light to trigger fluorescence at crime scenes?
blue at +/- 450 nm
footwear impression, hair, fibre, bloodstrains, latent prints, drugs, paint, grease, bones, teeth, bodily fluids
What is White Light?
White light is the light visible by the human eye. Visible light is usually defined as having a wavelength in the range of 400-700 nm.
What are the two types of Luminescence?
Fluorescence - luminenscence ceases shortly after exciting radiation is removed (6-10 secs)
Phosphoescence (Luminol, Blue Star) - luminescence continues for some time after exciting radiation is removed.
What is the Theory of Fluorescence?
Energy (light) is applied to an atom, which is absorved and excites the electrons altering their orbit around the nucleous. Fluorescene is caused when these excited atoms emit energy, usually at a higher wavelength (lower energy).
Explain the Stokes Shift
The difference between positions of the band maxima of the absorption and emission spectra of the same electronic transition.
What filters are required for Fluorescence?
Exciter Filter:
- placed in front of light source
- filters the output of a regular incandescent source to block unwanted wavelengths of light resulting in a coloured beam of light.
Barrier Filter:
- placed in front of eyes/camera
- allows desired light reflected fromt the subject to pass
What are the properties of Ultra Violet light?
- electromagnetic radiation with a wavelength shorter than that of visible light but longer than x-rays (10-400 nm)
- UV causes many substances to glow or fluoresce.
What does LASER stand for?
Light
Amplification by
Stimulated
Emission of
Radiation
What are the properties of Ardrox?
- UV light required
- simple mixing with methanol
- easy to use - rinse with water
- greenish colour
What are the properties of Basic Yellow 40 (Brillant Yellow)?
- requries FLS (450-485 nm)
- barrier filter KV550 (orange googles)
- easy to use - mix with ethanol, rinse with water
- yellow-green fluorescene
What are the properties of Rhodamine 6 G (R6G)?
- FLS - 505 - 535 nm
- barrier filter kv550 (orange goggles)
- easy to use - rinse with water
- green fluorescence
- LASER - 532 nm
What are the properties of DFO (1,8-Diazafluoren-9-one)?
- use with porous substrates
- FLS - start with 450 nm with barrier filter KV550 (orange goggles) proceed to 515 nm and 555 nm with barrier filter (red)
- LASER - best viewed with Laser 532 nm and barrier filter
- reacts with amino acids
What are the properties of 1,2-Indanedione Zinc Cl?
- alternative to DFO
- FLS - start at 450 nm with KV550 barrier filter, proceed to 515 nm a d 555 nm with red barrier filter.
- LASER - examine with 532 nm laser and laser specific barrier filter
- works better than DFO in high humidity areas
- reacts with amino acids (sweat)
What are the properties of Ninhydrin?
- reacts with amino acids (sweat) on porous substrate
- visible to naked eye
- works well on older prints and may continue to develop
- aqueous soluton dissolved amino acids
- signature is that it highlights pores
What are the properties of Silver Nitrate?
- based on reaction of soluble silver nitrate with NaCl, present in most latent fingerprints to form insoluble and light-sensitive silver cloride
- exposing silver chloride to UV light causes rxn to metallic silver, making impression visible
- can work with very old latent impressions
- destructive.
What are the properties of Oil Red O (ORO)?
- soluble lipid stain
- used on porous substrate
What are the properties of Physicak Developer?
- silver based liquid reagent which reacts with lipids, fats, oils, waxes present in fingerprint residue.
- should be last processes in chemical sequence
- can be used on exhibits that are wet or have been wet
- visible
How do Vacuum Metal Deposition (VDM) Chambers work?
- sensitive and works on very old fingerprints
- visible
- process can be time consuming
- equipement is expensive
- gold evaporated under pressure and coats substrate, believed to be absorbed by impression
- Zinc evaporated and bonds to gold background
- result in FR in colour of substrate and background grey
- only side treated at a time
What are three development mediums that can be used on the sticky side of tape?
- Gentian Violet
- Wet Wop - FP powder suspended in solution
- Titanium Dioxide - white coloured powder suspended in solution
What development medium can be used on wet non-porous substrates?
Molybdenum disulfide
- spray application
- power suspension
- visible grey or white
How can Cyanoacrylate be used to develop friction ridge impressions?
- monomer is super glue polymerizes with fingerprint residue (lipids/moisture)
- monomer vaporized by heat or reduced pressure
- fluorescent dyes will enhance visibility and help minimize background
- impressions will appear white
- due to spaghetti like strands of polymer reflecting and scattering light
- signature is that polymer an expand and form into furrows if over developed.
What information is included on a WHMIS workplace label?
Produced by the emloyer for use in the employer’s workplace only, and contains the following information:
- the identity of the product
- information for the safe handling of the product
- a statement that a material safety data sheet, if supplied or produced, is available
What information can be found on a WHMIS supplier label?
Product name
Risk phrases/warnings
Precautionary measures
First aid measures
Reference to MSDS
Name of supplier
