FORENSIC SCIENCE AND NANOTECHNOLOGY:
APPLYING NANOPARTICLES FOR VISUALIZING LATENT FINGERPRINTS
Matias Sametband, Prof. Daniel Mandler, Prof. Joseph Almog
Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
e-mail: sametm@pob.huji.ac.il
Silver physical developer (Ag-PD) is the standard reagent for developing latent fingerprints on
wet and porous surfaces such as paper. This method is based on the electroless deposition of
silver on the water insoluble residues of fingerprints creating a black silver deposit and enabling
the visualization of latent fingerprints. The Ag-PD solution is a meta-stable and complex solution
(a mixture of silver, ferrous and ferric ions and stabilizing surfactants) in which spontaneous
reduction of the silver ions often occurs degrading the solution ability for developing latent
fingerprints. This phenomenon is an acute problem for every forensic scientist who uses this
method.
The research objectives were:
1) Studying the Ag-PD instability by measuring different parameters which will lead to
new methods for stabilizing the solution. We have shown that the [FeII]/[FeIII] ratio decreases
with time due to oxidation of ferrous ions either by ambient oxygen or spontaneous oxidation by
silver ions in the solution. Two new methods were proposed for stabilizing the silver physical
developer: I) Argon bubbling: Inhibiting the oxidation of ferrous ions was accomplished by
bubbling Ar into the standard silver physical developer solution. II) “Two-step” procedure:
Separating between the silver and the ferrous ions made it possible to use these solutions even
two months after preparation.
2) Enhancement of latent fingerprints development through direct and indirect methods
using metal nanoparticles. This might lead to new and better methods than the standard Ag-PD
method. Gold nanoparticles (Au-NPs) stabilized with different alkanethiols dissolved in petrolether (2-3 nm) were used as nucleation sites for the deposition of silver. Fluorescent
nanoparticles: CdSe/ZnS nanoparticles stabilized with n-alkylamine dissolved in petrol-ether
adsorbed onto the ridges of the latent fingerprints fluorescing under UV illumination. These
nanoparticles adsorb onto fingerprint material, presumably by hydrophobic interactions, and
aggregation.
References:
A. Cantu, A. Leben and K. Wilson, Some advances in the silver physical development of latent
prints on paper. Proceedings of SPIE-The International Society for Optical Engineering (2003),
5071 (Sensors, and Command, Control, Communications, and Intelligence (C3I) Technologies
for Homeland Defense and Law Enforcement II), 164-167.
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D. Burow, D. Seifert and A. Cantu, Modifications to the silver physical developer. Journal of
Forensic Sciences 2003, 48:5:1094-1100
H. C. Lee and R. E. Gaensslen, Advances in Fingerprint Technology. 2nd Edition, Chapters 4 and
7, Jan 2001
Acknowledgment:
The US Technical Support Working Group (TSWG) and Israel's CSI department are
acknowledged for their support.
Organized and Produced:
http://www.isranalytica.org.il
P.O.B 4034 Ness-Ziona 70400
Tel.+972-8-940-9085, Fax. .+972-8-940-9086
Site: www.BioForum.org.il
E-mail: BioForum@bezeqint.net