Analysis of Latent Fingerprint Deposits by Infrared
`Microspectroscopy*
`
`DIANE K. WILLIAMS, REBECCA L. SCHWARTZ, and EDWARD G. BARTICK†
`Counterterrorism and Forensic Science Research Unit, FBI Academy, Quantico, Virginia 22135
`
`We report the use of infrared (IR) microspectroscopy for the anal-
`ysis of  ngerprint residues. The advantage of using an IR micro-
`scope lies in the ability to visualize and obtain spectra of individual
`particles and droplets that make up  ngerprint ridge deposits at a
`spatial resolution of approximately 10 mm. Our initial results sug-
`gest that infrared microspectroscopy in re ection–absorption mode
`provides reproducible spectral analysis of  ngerprint residue. Since
`infrared microspectroscopy is nondestructive to the sample, we will
`be able to study the changes in  ngerprint ridge deposits as a func-
`tion of time. The method holds promise for probing the difference
`between latent  ngerprints of adults and children.
`Index Headings: Infrared microspectroscopy; Latent  ngerprints;
`Forensic science.
`
`INTRODUCTION
`The examination of latent  ngerprints is an important
`aspect of crime scene investigations, but  ngerprints are
`not always recoverable or clear. In child abduction cases,
`children’s prints are often not obtained. Therefore, there
`is interest in the law enforcement community in  nding
`new methods of developing latent  ngerprints. To solve
`this problem, a better understanding of the chemical com-
`position of  ngerprint residue is crucial.
`The chemical composition and mechanisms of skin se-
`cretions from children and adults have been studied by
`diverse research groups using a variety of chromato-
`graphic methods.1–3 Early work on the differences in
`chemical composition of human skin surface lipids from
`birth to puberty was performed by Ramasastry and co-
`workers using thin-layer chromatography.1 Alexiou and
`co-workers measured the excretion of amino acids, am-
`monia, and proteins in the sweat of children using ion
`exchange chromatography.2 The study of skin surface lip-
`ids in children performed by Stewart and Downing in-
`volved the use of gas chromatography.3 For law enforce-
`ment purposes, research has been performed by Buch-
`anan, Asano, and Bohanon to study the chemical differ-
`ences in children’s and adults’  ngerprint secretions.4
`Their experiments were performed by analyzing the res-
`idue in  ngerprint ridges by gas chromatography–mass
`
`Received 26 August 2003; accepted 23 October 2003.
`* This is publication number 03-07 of the Laboratory Division of the
`Federal Bureau of Investigation. Names of commercial manufacturers
`are provided for identi cation only, and inclusion does not imply en-
`dorsement by the Federal Bureau of Investigation. Portions of this
`work were presented at the American Chemical Society-Congression-
`al Hearing, July 2000, in Washington, D.C., the 27th Annual Confer-
`ence of the Federation of Analytical Chemistry and Spectroscopy So-
`cieties, September 2000, in Nashville, Tennessee, and the 16th Meet-
`ing of the International Association of Forensic Sciences, September
`2002, in Montpellier, France.
`† Author to whom correspondence should be sent. E-mail: ebartick@
`fbiacademy.edu.
`
`spectrometry (GC/MS), and they concluded that the chain
`lengths are longer in the fatty acid esters in the  ngerprint
`residue of adults. Since the use of GC/MS involved sam-
`ple extraction, evaporation, and reconstitution, we have
`developed a method to analyze speci c chemical com-
`ponents in  ngerprint residue without any additional sam-
`ple preparation after collection.
`We report the use of infrared (IR) microspectroscopy,
`frequently referred to as microscopical infrared spectros-
`copy in the forensics community, for the analysis of  n-
`gerprint residue. The advantage of using an IR micro-
`scope lies in the ability to image individual particles and
`droplets that make up  ngerprint ridge deposits at a spa-
`tial resolution of approximately 10 mm. Infrared micro-
`spectroscopy is nondestructive to the sample, which al-
`lows for the study of variations in  ngerprint ridge de-
`posits over time.
`Research has been reported on the use of synchrotron-
`source infrared microspectroscopy for the study of latent
`human  ngerprints.5 However, we have found that con-
`ventional glowbar-source infrared microspectroscopy has
`demonstrated suf cient sensitivity and spatial resolution
`to obtain spectra with adequate signal-to-noise ratios. The
`bene t of the glowbar-source technique is the potential
`of using a portable Fourier transform infrared (FT-IR )
`spectrometer in the  eld, which is impossible with current
`synchrotron-based technology.
`
`EXPERIMENTAL
`
`Re ection mode was chosen for experimentation due
`to the ease of sample collection and sample storage. For
`re ection–absorption experiments, the samples were ob-
`tained by having research volunteers deposit  ngerprints
`on aluminum-coated slides. One  ngerprint was obtained
`prior to washing of hands, one print was obtained after
`hands were washed and rinsed for approximately  ve
`minutes with water, and a third print was obtained after
`washing, rinsing, and rubbing the fore nger across the
`forehead. Since the hands do not contain sebaceous
`glands, the skin surface residue on the hands comes from
`eccrine glands in the epidermis.6 Therefore, the print ob-
`tained from washed hands should be free of sebaceous
`material. The print obtained after touching the forehead
`would contain sebaceous material since there is a high
`density of sebaceous glands in the forehead region.6
`The  ngerprint deposits were observed using either a
`153 or 323 objective on the microscope. Under the mi-
`croscope, there were two distinct types of residue ob-
`served: droplets and solid particles. Typically, a single
`droplet or particle was selected and the aperture was set
`according to the size of the droplet or particle. Spectra
`were collected at 4 cm 21 resolution and averaged for 128
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`Applied Spectroscopy
`Volume 58, Number 3, 2004
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`FIG. 1. Micrograph and corresponding spectra of an eccrine  ngerprint deposit obtained from an adult male.
`
`scans. A liquid-nitrogen-cooled MCT-High D* detector
`with a response range of 4000 –800 cm 21 was used.
`For attenuated total re ection (ATR) mode experi-
`ments, the sample collection was identical to that for re-
` ection–absorption mode, and analysis was performed
`using a Thermo Nicolet Corporation In nity Seriesy Di-
`amond ATR objective.
`
`RESULTS AND DISCUSSION
`Optimization of Instrument Parameters. To deter-
`mine the optimum conditions for obtaining spectra using
`microscopic FT-IR, experiments were performed in re-
` ection–absorption and ATR modes. The results indicate
`that re ection–absorption mode is the preferred method
`for obtaining spectra of  ngerprint residue because no
`appreciable signal was detected in ATR mode. The lack
`of results using the ATR mode probably results from the
`fact that  ngerprint ridges are not deposited as continuous
` lms but as individual droplets and particles.
`A visual comparison of skin surface residue deposits
`suggests that very little residue is deposited in eccrine
`prints when the hands are washed before collection.
`However, even with a small amount of material, we were
`able to limit the analysis to individual droplets within the
` ngerprint ridge and record spectra. To determine the op-
`timum conditions for obtaining these spectra, both the
`153 and 323 microscope objectives were used. The re-
`sults indicate that the use of the 323 microscope is pref-
`erable due to the ability to visualize the smaller particles
`without signi cant
`loss of signal. The typical aperture
`size used with the 323 objective was 20 3 20 mm, al-
`
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`Volume 58, Number 3, 2004
`
`though the aperture was changed to adapt to the size of
`the droplet/particles under study.
`Sebaceous prints contain greater amounts of material
`than eccrine prints, although the diameters of the solid
`particles do not vary signi cantly from those found in
`eccrine prints. Therefore, it was determined that for all
`of our experiments involving  ngerprints, the 323 ob-
`jective would be used.
`The data revealed that 128 scans were suf cient to
`produce spectra with peak-to-peak signal-to-noise ratios
`of more than 100 to 1 for most prints studied. For eccrine
`prints with very little material deposited, 1000 scans were
`sometimes required to enhance the signal-to-noise ratio.
`Eccrine Analysis. Figure 1 shows a representative pho-
`tomicrograph and corresponding spectra of  ngerprint res-
`
`TABLE I. Characteristic frequencies and vibrational modes ob-
`tained from a particle in the eccrine  ngerprint deposit of an adult
`male.
`
`Frequency
`(cm 21)
`
`3281
`1741
`1655
`1546
`
`1463
`
`1379
`1233
`1160
`1113
`
`Vibration
`
`N–H stretch (secondary amide)
`C5O stretch (saturated ester)
`C5O stretch (secondary amide)
`Major: N–H in-plane bend (secondary amide)
`Minor: C–N stretch
`CH 3 asymmetric bend
`CH 2 symmetric bend
`CH 3 symmetric bend
`C–N stretch (secondary amide)
`C–C–O stretch (saturated ester)
`O–C–C stretch (saturated ester)
`
`

`

`FIG. 2. Micrograph and corresponding spectra of a sebaceous  ngerprint deposit obtained from an adult male.
`
`idue that was obtained from an adult male after the hands
`were washed. The spectrum labeled A is characteristic of
`spectra that were obtained of eccrine secretions of adults.
`To determine the chemical composition of the droplet, the
`position and intensity of the peaks were compared to li-
`brary spectra of biological compounds. Since a match was
`not found, the peak positions and intensities were analyzed
`to determine the functional groups present in the droplet.
`The most notable feature in the spectrum is the C–H
`stretching vibration just below 3000 cm 21. At 1741 cm 21,
`a peak corresponding to a carbonyl stretching vibration is
`apparent and contains a shoulder at 1713 cm 21, which is
`likely due to the presence of a second carbonyl stretching
`mode. At 1463 cm 21, there is a peak corresponding to a
`methyl asymmetric bend. The peak assignments suggest
`that the chemical composition of the droplet represented
`in spectrum A is an ester of a dicarboxylic acid, and this
`result is consistent with results obtained by Buchanan, As-
`ano, and Bohanon, who detected the presence of acid es-
`ters in adult  ngerprint residue using GC/MS.4
`The spectrum labeled B is characteristic of the dark
`particles deposited in eccrine  ngerprints. To determine
`the chemical composition of the dark particle shown in
`Fig. 1, peak assignments were made and are shown in
`Table I. The peak assignments shown in Table I suggest
`the presence of a secondary amide, which would be char-
`acteristic of protein-containing skin cells. Eberhardt7 pre-
`sumed that solid particles visually observed in micro-
`scopic studies of skin surface residue were remainders of
`cell walls from oil-secreting glands and these spectral re-
`sults support the presumption. Additional peaks in the
`spectrum suggest the presence of saturated esters.
`
`Sebaceous Analysis. Figure 2 shows a representative
`photomicrograph and corresponding spectra of  ngerprint
`residue that was obtained from an adult male when the
`forehead was touched after the hands were washed. The
`droplet shown in Fig. 2A (point 4) is chemically similar
`to the droplet shown in Fig. 1A. The major difference in
`the two spectra labeled A is the intensity of the peaks,
`which is a function of the amount of material deposited.
`The composition of the solid particle (point 1) is chem-
`ically similar to the particle that was present in the ec-
`crine  ngerprint shown in Fig. 1B. The major difference
`between spectrum B of the eccrine material and spectrum
`B of the sebaceous material, shown in Fig. 2, is the pres-
`ence of a peak at 1713 cm 21. The presence of this peak
`is attributed to the carbonyl stretching vibration of an
`acid ester.
`It has been reported that squalene is the major com-
`ponent in skin surface residue in  ngerprints of adults,4
`but our results indicate that pure squalene is not the major
`component. Squalene is an acyclic triterpene and will un-
`dergo oxidation in the presence of bacteria to form a
`dicarboxylic acid.8 These preliminary spectral
`results
`suggest that squalene oxidation products are a likely com-
`ponent in adult  ngerprint residue since an acid ester can
`be produced from esteri cation of a dicarboxylic acid.9
`
`CONCLUSION AND FUTURE WORK
`
`The capability of using infrared microspectroscopy to
`study  ngerprint ridge deposits has been demonstrated.
`The reproducibility of the method has been tested and the
`random variation in the analytical signal was less than
`
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`
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`10%. Relative to GC/MS, there are several inherent ben-
`e ts of using infrared microspectroscopy to study the
`composition of residue in  ngerprints, but the major ben-
`e t is the ability to retain the  ngerprint for time studies.
`Now that the ability to analyze  ngerprint residue by
`microscopic FT-IR has been demonstrated, current work
`is focused on using the technique to study differences in
`children’s  ngerprint residue. It has been indicated that
`latent  ngerprints of children disappear more quickly
`than those of adults4 and as a result, there is signi cant
`interest in the forensic community to understand how the
`chemical composition of children’s
` ngerprints may
`change with time so that new methods of processing chil-
`dren’s  ngerprints may be developed.
`
`1. P. Ramasastry, D. T. Downing, P. E. Pochi, and J. S. Strauss, J. Invest.
`Dermatol. 54, 139 (1970).
`2. D. Alexiou, A. Anagnostopoulos, and C. Papadatos, Am. J. Clin.
`Nutr. 32, 750 (1979).
`3. M. E. Stewart and D. T. Downing, J. Invest. Dermatol. 95, 605
`(1990).
`4. M. V. Buchanan, K. Asano, and A. Bohanon, Proc. SPIE-Int. Soc.
`Opt. Eng. 2941, 89 (1997).
`5. T. J. Wilkinson, D. L. Perry, M. C. Martin, and W. R. McKinney,
`Abstract Paper, Am. Chem. Soc. 222 (2001).
`6. P. Clarys and A. Barel, Clin. Derm atol. 13, 307 (1995).
`7. H. Eberhardt, Arch. Dermatol. 251, 149 (1974).
`8. C. W. Seo, Y. Yasuhiro, N. Takada, and H. Okada, Appl. Environ.
`Microbiol. 45, 522 (1982).
`9. R. T. Morrison and R. N. Boyd, Organic Chemistry (Allyn and Ba-
`con, Inc., Boston, MA, 1973).
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