Basic Yellow 40 (BY40)
Definition
A fluorescent dye (excitation 450-490 nm, emission ~530 nm) applied immediately after CA fuming with a simple aqueous rinse to remove excess; used at the Netherlands Forensic Institute and Northern European national labs for light-substrate work.
- Type
- Fluorescent dye stain
- Excitation
- Approximately 450 to 490 nm
- Emission
- Approximately 530 nm
- Applied after
- Cyanoacrylate (CA) fuming
Common questions
Why is BY40 applied after CA fuming rather than on its own?+
CA fuming first polymerises onto the ridge detail of a latent print, and BY40 then binds selectively to that polymer, which gives a fluorescent contrast that is far stronger than staining unfumed ridge residue directly. The fuming step is what makes the dye effective.
What substrates suit BY40 best, and where does it fall short?+
It performs well on light-coloured, non-porous or semi-porous substrates where fluorescence under alternate light provides contrast that visual examination alone would miss. On very dark or highly fluorescent substrates the dye's signal can be masked by background fluorescence, and an alternative stain may work better.
Related terms
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- Barrier Filter
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- Cyanoacrylate (CA) Fuming
- The development of latent prints on non-porous surfaces by exposing the item to ethyl or methyl cyanoacrylate vapour in a humidity-controlled environment;...
- Ethyl Cyanoacrylate (ECA)
- The active monomer in forensic CA fuming products and most consumer Super Glue formulations; undergoes anionic polymerisation initiated by nucleophiles (water, amines)...
- Inherent Fluorescence
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- Lumicyano
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- Rhodamine 6G
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