The document discusses two methods for developing latent fingerprints through alternative light sources: 1) Post-treatment of developed fingerprints with luminescent powders or dyes that fluoresce under laser light, intensifying the ridge detail. Commonly used materials include acridine orange, rhodamine B, and lanthanide complexes. 2) Developing fingerprints chemically by applying reagents that react with amino acids in sweat to form fluorescent compounds, such as ninhydrin forming Ruhemann's Purple or fluorescein forming luminescent derivatives. Zinc chloride treatment improves ninhydrin results and some lanthanide complexes provide longer fluorescence.

2. Development of Latent fingerprints through
Alternative light sources (Part-II)
By-
Vaishnavi Puli
Member of Applied Forensic Research
Sciences

3. Content
• Post-treatment of developed fingerprints with
luminescent materials.
• Post-treatment of developed fingerprints with reagents
form luminescent reaction products.
• MCQ

4. Post-treatment of developed fingerprints with
luminescent materials
• In this procedure the fingerprint impression is treated with a laser active substance
which becomes physically adsorbed on the sweat residue. When illuminated with the
laser light the ridge pattern produces a contrast visibles the background.
1.Powders method-
• Application of finely divided material and the subsequent removal of extra powder
by brushing, blowing and tapping has been the universal method of intensifying
fingerprints on non-absorbing surfaces since the early days of fingerprint
technology.
• The technique relays on the mechanical adherence of fingerprint powder to the
moisture component of this can ridge deposit.
• Conventional fingerprint powders consists of resinous polymer for adhesion and
colourent for contrast. The adhesive get absorbed in the moisture component of
fingerprint and the colourent gets absorbed on the adhesive.

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• The commonly used adhesives are starch , kaolin, rosin and silica gel.
• The colourent may be an inorganic salt like Manganese dioxide, or an organic
derivative lke eosin blue.
• A good no.of powder formulations contain organic derivatives that flourish or
phosphorisis upon exposure to laser light, such compositions are useful for
visualization of fingerprint deposited on multi colored surfaces that for present
contrast problem if developed with conventional powders.
• Moreover, they can be used for developing weak prints also.
• Some common organic compounds which have been used for preparing luminescent
powders are Acridine orange, Acridine Yellow, Crystal violet, and rhodamine B.
• Lanthanide complexes offer several advantages including benefits from large Stokes
shape, long luminescence lifetimes, narrow emissions, ability of sequential assembly
of complexes and chemical variability of ligands.
• Moreover such powders are suitable for detection of latent fingerprints on difficult
surfaces such as wood, masking tape and polythene.

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.
2. Cyanoacrylate method-
• The principle underlined the cyanoacrylate method also called as "Super-glue fuming"
or " super glue technique" depends on the fact that when 'alkyl-2-cyanoacrylate reagent
is allowed to vapourise it undergoes polymerization.
• The polymerised ester has a tendency to get adsorbed on the sweat residue imparting a
white color to the ridge pattern.
Mechanism leading to

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• A China dish containing a few drops of cyanoacrylate and sodium hydroxide
solution is placed in a fuming cupboard or a fuming chamber.
• The object bearing the latent prints are suspended from the roof of the
cabinet.The item is exposed to cyanoacrylate vapours for about two hours until
whitest coloured fingerprint pattern develops.
• Even though cyanoacrylate fuming is a convenient fingerprints the developed
imprints are white in color and therefore, lack contrast.
• The contrast may be enhanced by post-treatment of cyanoacrylate developed
prints with a solution of luminescent dye such a stains flourish upon exposure to
laser light revealing sharp fingerprints.
• When dye solutions alone are used for print processing the results are not
satisfactory, the reason being the dye solution tends to washout the sweat.
However when stains are used in conjunction with cyanoacrylate fuming this
Problem is avoided. The cyanoacrylate Polymer stablizes the latent fingerprints
so that solution dye doesn't wash it away.

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• Crystal violet improves the contrast of weak prints developed on polythene by
cyanoacrylate method. The stains get selectively absorbed on the polymerised
cyanoacrylate.
• Likewise, the Rhodamine-6G treated prints also get preferentially adhered to the
polycyanoacrylate deposition and hence, are suitable for laser examination.
Moreover, the absorption spectrum of the stain matches with blue-green
illumination of argon laser.
Super Glue Fuming
Chamber
Crystal
Violet
Rhodamine-6G

9. Post-treatment of developed fingerprints with reagents form
luminescent reaction products
• The Amino acids present in the sweat deposition may be transformed into luminescent
derivatives by treatment with the chemical reagents.
• The luminescent compounds when examined under laser reveal the ridge pattern of the
fingerprints . So here we have some methods:
1. Ninhydrin method:
• The Ninhydrin method has traditionally being the most popular one for processing
latent fingerprints on porous absorbent surfaces like paper, cardboard and wood.
• The method relays on the reaction of ninhydrin with AA's of the fingerprint residue. The
reaction produces "purple" coloured compound called as "RUHEMANN'S PURPLE"
which becomes deposited along the ridge making the prints visible.
• A 0.2-1.5% solution of Ninhydrin in freon 113 is sprayed on the exhibit from a distance of
about 6 inches. After the solute evaporates the solution is resprayed.
• The surfaces are then heated up to 80° C without allowing it to come in contact with the
heat source.

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Structure of ninhydrin & Ruhemann's Purple
fingerprint
• Better results are obtained by steaming the article for optimum development of
fingerprints at a relative humidity of 65-80% .
• The AA's in the sweat residue neither interact with the cellulose content of the paper
nor would do they migrate with in capillaries of the substrate.
• Therefore, the ninhydrin makes it possible to develop the fingerprints that are many
year's old. Since, the AA concentration in the sweat residue is quite low the
developed prints do not normally show a sharp contrast.
• In order to improve the working performance of ninhydrin reagent the developed
prints are post treated with group 12 metal salts. This interaction converts the non-
flourescent Ruhemann's Purple into a photo luminescent complex.

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• The fingerprints developed by ninhydrin Zinc Chloride method becomes highly
flourescent under argon laser light.
• The 480nm line of argon laser is appropriate for excitation of the "Orange Zinc
Ruhemann's Purple" complex that absorbs 485nm and emit 560nm of wavelength.
Photoluminescent Complex
Graph showing absorption wavelength of
Orange Zinc Ruhemann's Purple
complex

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• As a result a pronounced improvement in their detectibility observed. Moreover,
with Zinc Chloride post-treatment and argon laser examination the Ninhydrin
method may extended to the detection of latent fingerprints on non-porous
surfaces like glass and stainless steel.
• The complexes formed by the combination of Ruhemann's Purple with
Eurobium, Turbium salts to have been found suitable for fingerprint
development particularly on flourescent surfaces.
• These complexes show enhancement of Lanthanide luminescent via
intramolecular energy transfer. Moreover the lifetime of the luminescence is
much longer than that of the usual background flourescence. Lanthanide
complexes are therefore suitable for time resolved luminescent imaging.

13. 2. Flourescamine Method
• Likewise, Ninhydrin the flourescamine reagent too reacts with AA content of sweat
residue producing luminescent reaction products which render visibility to the
fingermark.
• A solution of 20mg of flourescamine and 0.4ml triethylamine in 100ml acetone is
sprayed on the surface containing the fingermark.
• After the surface dries it is observed under Argon-laser.
• Experience has shown that flourescamine not only posses a greatest sensitivity than
the Ninhydrin but also works well for the detection of latent fingermarks on
multicolored surfaces.
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Structure of Flourescamine