New Reagents for Development of Latent Fingerprints.


Series: NIJ Update
Published: September 1995
4 pages
7,092 bytes


A form of physical evidence always welcomed by
prosecutors, fingerprints are unique records that
can confirm the identity of a crime's perpetrator.
Technically, fingerprinting is a biochemical method
for determining the structure of a protein in which
the protein is split into peptides by digestion
with protease, and the fragments are separated in
one direction by electrophoresis and at right
angles by chromatography. After staining with a
reagent, the peptide fragments are seen to be in
characteristic locations. Improving the processes
for obtaining usable prints as evidence has led to
a search for superior development reagents to aid
in identifying latent fingerprints. National
Institute of Justice (NIJ)-sponsored research found
ways to enhance the properties (e.g., line
resolution, fluorescence) of one of the most
commonly used reagents, ninhydrin, via structural
modifications. In addition, ninhydrin analogs were
altered to expand their solubility to a wider range
of organic solvents. 

Previous work on ninhydrin

Ninhydrin was first prepared in 1910 by the English
chemist, Siegfried Ruhemann, who also investigated
the formation of the violet compound (Ruhemann's
Purple, or RP) produced by ninhydrin's reaction
with amino acids. The significance of this
discovery to forensic science went unnoticed until
1954, when Oden and von Hoffsten reported the use
of ninhydrin as a fingerprint developing reagent
that reacts with amino acids secreted from sweat
glands. Although the content of amino acids in a
fingerprint residue is low (compared to the content
of salts and fatty acids), the RP produced from the
reaction of these amino acids with ninhydrin is
deeply colored, and the developed fingerprints are
usually highly visible. Thus, ninhydrin has long
been known as one of the most affordable and useful
reagents for visualization of latent fingerprints
on porous surfaces (such as paper, wood, and
walls).

In cases where the developed fingerprints are weak,
secondary treatment with an aqueous zinc chloride
solution can improve the print's line resolution
quality. Zinc chloride-treated prints can be
observed as "glowing" (fluorescent) when
illuminated with light of a certain wavelength. In
1990, C. A. Pounds and coworkers introduced the
reagent 1, 8-diazafluorenone (DFO), which is
commercially available and used in the United
Kingdom. Unlike ninhydrin, DFO gives a weakly
colored initial print; the main feature of this
reagent is its ability to give a fluorescent print
without secondary treatment. However, some
investigators currently report difficulties with
uniform print development using DFO.

Synthesis of new ninhydrin analogs

The NIJ-sponsored research group had previously
prepared a compound, thieno[f]ninhydrin, that
provided an initial print as deeply colored as one
produced with ninhydrin as the reagent. 
Thieno[f]ninhydrin also displayed excellent
fluorescent properties without requiring the use of
a metal for secondary development. However, the
organic compound was both difficult and expensive
to produce on a commercial scale. Nevertheless, the
new reagent indicated that the thienyl fragment
could be one of the desirable structural features
to incorporate into the ninhydrin molecule.

Until recently, protocols available for synthesis
of ninhydrin analogs were inefficient. The research
group reported novel approaches to the synthesis of
benzo[f]-ninhydrin, 5-methoxy-ninhydrin,
5-(methylthio)ninhydrin, thieno[f]ninhydrin, as
well as to the extended series of 5-phenyl- and
5-thienylninhydrin derivatives, starting from the
inexpensive bromoxylene in a short high-yielding
synthetic sequence. When tested,
5-(2-thienyl)ninhydrin and 5-(3-thienyl)ninhydrin
(2-THIN and 3-THIN) displayed properties (i.e.,
brighter fluorescence, better line resolution)
superior to ninhydrin's as fingerprint developing
reagents.

Chemical modifications facilitating the choice of
solvent

Ninhydrin is commonly used for fingerprint
development on porous surfaces, which are dipped in
the reagent solution or sprayed with it. The choice
of solvent is important--different kinds of inks on
documents can be affected by the solvent employed;
the fingerprint itself can be smeared by an
inappropriate solvent. Solvents used in forensic
science must pose no more than a minimal safety
risk, in terms of properties such as flammability
or toxicity, and they must also be environmentally
safe. Chlorofluorocarbons, such as
trichlorofifluoroethane, had been the solvents of
choice in ninhydrin formulations. When banned
recently by the Environmental Protection Agency, a
search was begun for acceptable substitute
solvents. In the ninhydrin study, researchers found
that some derivatives of the reagent, resulting
from its reaction with higher molecular weight or
"long chain" alcohols (i.e., hemiacetals), undergo
the same color-forming reactions as ninhydrin, but
they are substantially more soluble in organic
solvents (e.g., ethyl acetate, methylene chloride,
or toluene).  Hemiacetals can be quantitatively
obtained from any ninhydrin analog in a one-step
procedure.      

Practical implications

Several synthetic approaches were developed and
evaluated to provide a total of 21 new ninhydrin
analogs. These reagents were evaluated for
fingerprint visualization by forensic experts at
the U.S. Secret Service and other law enforcement
agencies, both in this country and in England,
Switzerland, Australia, and Israel.  The new
methodology afforded two complementary reagents
(2-THIN and 3-THIN), which displayed superior
fingerprint developing properties. Large-scale
production of 2-THIN has been initiated by Vinfer
Ltd., a Northern Ireland manufacturer, to
investigate its potential for commercialization.

This research has provided a viable solution to
problems encountered by criminalists as a result of
the prohibited use of chlorofluorocarbons.

Notes
1. Ruhemann, S., Trans. Chem. Soc., 97 (1910):2025.
2. Oden, S. and B. von Hofsten, Nature, 173
(1954):449.
3. Pounds, C.A., R. Grigg, and T.
Mongkolaussavaratana, Journal of Forensic Sciences,
35 (1990):169-175.
4. Cantu, A., D.A. Leben, M.M. Joullie, and R.R.
Hark, Journal of Forensic Identification, 43
(1993):44-66.
5. Hark, R.R., D.B. Hauze, O. Petrovskaia, M.M.
Joullie, R. Jaouhari, and P. McComiskey,
Tetrahedron Letters, 35 (1994):7719-7722.

This project was supported by NIJ grant 92-IJ-CX-
K0154. The researchers were Professor Madeleine M.
Joullie, Department of Chemistry, University of
Pennsylvania, and associates.  An unpublished
report will be available in about 6 months through
interlibrary loan, or a xeroxed copy can be
provided for a small fee. Contact the National
Criminal Justice Reference Service at 800-851-3420
for information.