Visualization of latent fingermarks by nanotechnology: Reversed development on paper-a remedy to the variation in sweat composition

Article abstract of DOI:10.1002/anie.201205259

Don't sweat it: Negative fingermarks are developed on paper by the application of gold nanoparticles (gold circles) that are capped by a bifunctional ligand, and then silver precipitation. In this process, paper is the substrate and the fingermarks serve as a mask. This approach may contribute to the successful recovery of latent fingermarks by law enforcement agencies. Copyright

Full text of DOI:10.1002/anie.201205259

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Angewandte
Communications
DOI: 10.1002/anie.201205259
Gold Nanoparticles
Visualization of Latent Fingermarks by Nanotechnology: Reversed
Development on Paper—A Remedy to the Variation in Sweat
Composition**
Nimer Jaber, Adam Lesniewski, Hadar Gabizon, Sanaa Shenawi, Daniel Mandler,* and
Joseph Almog*
Paper is one of the most frequently tested surfaces for the
detection of latent fingermarks in criminal and terrorist-
related investigations. Despite the plethora of modern
physical and chemical fingerprint-detection techniques,[1]
a considerable portion of the latent fingermarks still escape
detection. A plausible explanation is the remarkable differ-
also in forensic science, as visualizing reagents for latent
fingermarks.[3]
Accumulative results on a large number of paper items
such as used checks, all of which are supposed to bear latent
fingemarks, have shown that over 50% escape detection of
identifiable marks.[4] Such observations have led to intensive
research into more-sensitive fingerprint detection techniques.
Paper that has been wetted is a particular challenge since the
amino acids, which are the main substrate for chemical
enhancement of latent fingermarks, are dissolved and
removed by the water.
A silver physical developer (Ag-PD), comprising an
aqueous solution of silver nanoparticles (AgNPs) stabilized
by cationic surfactants, is required to achieve satisfactory
development of such fingermarks. Silver slowly deposits on
the water-insoluble components of the sweat, forming dark
grey to black impressions (Figure 1).[5] Although the tech-
nique is quite sensitive, it suffers from
ence in sweat composition between individual persons.[2]
A
potential remedy to this problem could be achieved by
reversing the roles, that is, developing a fingerprint-detection
technique in which paper serves as the substrate for the
interaction with the reagent, while the latent fingermarks will
serve as a mask.
In this work, “negative” fingermarks have been developed
on paper, even after soaking in water, by the application of
a new bifunctional reagent attached to gold nanoparticles
(AuNPs), and then a silver physical developer (Ag-PD). The
bifunctional reagent is composed of an active head, that is,
a polar group with high affinity to cellulose, attached by a long
chain to an active tail containing a sulfur group, which can
stabilize AuNPs. Through the active head, the AuNPs, which
are stabilized by the active tail, adhere preferentially to the
paper cellulose rather than to the fingerprint material, to
which they conventionally bind. Consequently, Ag-PD, which
normally develops sebaceous fingermarks by precipitating
dark silver on the sebaceous material, precipitate preferen-
tially on the gold-coated areas giving rise to the appearance of
uncoloured ridge detail on a dark background. In this
competing process, the paper itself serves as the substrate,
whereas the fingermarks serve as a mask. This process may
increase the overall yield of developed fingermarks as it
bypasses the issue of the remarkable differences in sweat
composition between individual persons.
several inconveniences, including
complexity, lack of reproducibility,
solution instability, and often poor
contrast.[1,3a,5,6]
As a result, many forensic labo-
ratories refrain from using this tech-
nique on a routine basis. Latent
fingermark enhancement by gold
nanoparticles stabilized by citrate
ions in aqueous medium, and then
a modified Ag-PD, is currently used
Figure 1. Sebaceous
in a process known as colloidal gold
or multimetal deposition (MMD).[7]
AuNPs adhere to the fingermark
residue and catalyze the precipitation
fingermark developed
by Ag-PD.
Functionalized nanoparticles have drawn great interest
during the past decade not only in potential applications as
biomedical, electronic, catalytic, and optical materials, but
of metallic silver from the Ag-PD solution. The gold
adherence to the fingermark material is explained by an
ionic interaction between the negatively charged gold colloids
and the positively charged components of the fingermark
residue at low pH.[7] In a modification known as SMD (single-
metal deposition), the enhancement of gold colloids by
precipitation of silver, was replaced by gold-based growth of
the nanoparticles.[7a] Several other fingerprint techniques that
are also based on nanochemical processes, have been
suggested recently; all of these suggestions involve the
adherence of nanoparticles to the fingerprint material.[1,3,8]
Previously we showed that good quality fingermarks were
developed by treatment with an organic solution of hydro-
phobic AuNPs stabilized by long chain thiols, and then with
[*] Dr. N. Jaber, Dr. A. Lesniewski, H. Gabizon, S. Shenawi,
Prof. D. Mandler, Prof. J. Almog
Institute of Chemistry, The Hebrew University of Jerusalem
Jerusalem 91904 (Israel)
E-mail: almog@mail.huji.ac.il
daniel.mandler@mail.huji.ac.il
[**] The authors wish to thank the US Technical Support Working Group
(TSWG) for providing the financial support to this project.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201205259.
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Chemie
Ag-PD.[3b] The fingerprint ridge details appear as dark
impressions on a light background owing to the catalytic
precipitation of silver onto the gold. Like the Ag-PD and
MMD techniques, however, this process too suffered from
similar inconsistency, which can be at least be partially
ascribed to the great variability in fingerprint residue
composition.[2] As papers are composed of cellulose fibres,
a method based on AuNPs–cellulose interactions should be
highly versatile and reproducible. This approach requires
bifunctional reagents, whose molecules contain active heads
that have a high affinity to the paper, and active tails that can
bind to the metallic nanoparticles. We prepared the bifunc-
tional compound 1, which was attached to AuNPs to form 2
(Scheme 1). Preferential binding of the AuNPs 2 to the paper
was achieved through the active head, an acyl pyridazine, at
the other end of the alkyl chain.
Figure 2. Latent fingermark development by treatment with 2, followed
by Ag-PD.
Scheme 1. Synthesis of 1 and 2. a) CH3CN, 858C, 18 h, N2. b) CH2Cl2,
SOCl2, reflux. c) CH2Cl2, RT. d) Toluene, 24 h stirring, RT. TOAB=
tetraoctylammonium bromide.
The AuNPs were efficiently adsorbed onto the entire
paper surface (invisible to the naked eye), however, leaving
the sebaceous ridges uncoated (Figure 2). A secondary treat-
ment with conventional Ag-PD (see the Supporting Informa-
tion for details) caused the precipitation of black silver on the
gold-coated regions, but the sebaceous ridges remained
uncoloured. Thus, the outcome of the entire process was
uncoloured fingermarks on a dark background, thus having
a reversed or negative appearance.
The process is fast; optimal development was usually
obtained after 5 min of treatment with 2, followed by 40–60 s
treatment with Ag-PD (Figure 3). If the exhibits are left in the
Ag-PD solution for a longer period of time, silver will
precipitate eventually on the ridges as well, thus reducing the
contrast (Figure 4). This phenomenom is explained by the
occurrence of the regular Ag-PD reaction, in which the
Figure 3. A fresh sebaceous fingermark (after soaking in water for
5 min and drying under air) developed by treatment with 2, followed
by Ag-PD.
AgNPs, which are stabilized by cationic surfactants, are
stripped by the lipid fraction of the fingermarks, thus resulting
in the precipitation of black silver on the fingermarks.[5b] This
process apparently is much slower than the catalytic precip-
itation by AuNPs, and enables us to achieve a reverse
development with good contrast. Working conditions are
currently being optimized in regards to concentrations,
immersion periods, and type of paper, as well as further
modification of the ligand.
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that the reversed appearance of the fingerprints results from
interactions of the polar substituent at the other end of the
thiol chain. The process is quite robust, and even partially
degraded Ag-PD solutions produce good results.
Notably, the VMD (vapour metal deposition) technique
also develops negative fingermarks, but on nonporous
surfaces, particularly polyethylene and polypropylene. This
method, which is based on vapour-phase coating with gold,
and then zinc, under high vacuum, is considered the most
sensitive fingerprint technique for these substances.[10]
In summary, by modifying the thiolic ligands, which
stabilize the AuNPs, we were able to reverse the affinity of
the AuNPs to the substrate, and hence to develop good
quality negative fingermarks. The method presented here
differs from existing techniques that are based on nano-
technology, by a major characteristic: the substrate for this
reaction is paper itself and not the fingermarks; gold is
attached preferentially to the paper and the fingermarks
develop in a reversed mode, that is, the reaction occurs
around the ridges and between them, but not on them.
Optimization of this process is underway.
Figure 4. Fresh sebaceous fingermarks (soaked in water for 5 min and
dried under air) developed by treatment with 2, followed by immersion
in Ag-PD solution for various periods of time.
Fingermarks containing relatively little tallow also devel-
oped well. Eccrine fingermarks however, could not be
visualized by this technique, and gave rise to total darkening
of the paper. We assume that pure eccrine material does not
form an efficient mask and therefore does not prevent the
active heads from binding to the paper.
The mechanism of the immobilization of 2 on paper
surface is most likely hydrogen bonding between the active
head and cellulose. To support (or refute) the hydrogen-
bonding hypothesis, we carried two sets of experiments. The
first set involved the synthesis and testing of AuNPs capped Experimental Section
Sebum-rich (sebaceous) fingermarks were obtained from several
with bifunctional ligands. Some of the ligands had functional
end groups that are known to form hydrogen bonds (glucose,
acetylthioalkoxy bezaldehydes, and w-mercaptocarboxylic
acids,(should be:…carboxylic groups, respectively) having
hydroxy, formyl, or carboxylic groups) and some had polar
end groups that cannot participate in hydrogen bonding, for
example, tetrachlorobenzene, or had no functionalized end
groups at all (long chain thiols, as in Ref. [3b]). Each
functionalized AuNP was tested for the visualization of
sebaceous fingermarks on paper by the described technique.
We found that “negative” fingermarks were developed
exclusively by nanoparticles of the first group ,that is, those
that could form hydrogen bonds, whereas the second group
developed the common “positive” fingermarks.
volunteers by rubbing their fingers against the forehead and stamping
them onto A4 paper strips. The paper strips bearing the sebaceous
prints were immersed in an acetonitrile solution of 2 containing 0.5%
dimethylsulfoxide (prepared by dissolving the AuNPs in a small
amount of dimethylsulfoxide and diluting with acetonitrile) for
periods ranging from 10 s to 5 min, followed by development with
Ag-PD. Best results were obtained by immersion in Ag-PD for
approximately 50 s. Yet, the decision of when the fingerprint is
sufficiently developed should be made by observation. It is important
to rinse the paper in water immediately after the Ag-PD treatment.
Received: July 4, 2012
Revised: August 28, 2012
Published online: November 4, 2012
The second set of experiments comprised the removal of
the AuNPs from the treated paper by solvent. The efficiency
of the removal was tested by subsequent dipping in Ag-PD
solution. Fast darkening of the paper indicated that the
removal was incomplete. We found excellent correlation with
the previous set of experiments, that is, effective removal of
AuNPs of the first group (containing hydrogen bonding end
groups) required harsh conditions involving shaking the
paper in Vortex in aqueous methanol, whereas removal of
AuNPs of the second group was achieved by gentle shaking
with petroleum ether.
Keywords: bifunctional reagents · gold · latent fingermarks ·
multimetal deposition · nanotechnology
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An alternative explanation to the reversed appearance of
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