TECHNICAL NOTE
`
`CRIMINALISTICS
`
`J Forensic Sci, March 2010, Vol. 55, No. 2
`doi: 10.1111/j.1556-4029.2009.01262.x
`Available online at: interscience.wiley.com
`
`Kimone M. Antoine,1,2 B.S.; Shirin Mortazavi2; Angela D. Miller,3 M.S.;
`and Lisa M. Miller,2 Ph.D.
`
`Chemical Differences Are Observed in
`Children’s Versus Adults’ Latent Fingerprints
`as a Function of Time*
`
`ABSTRACT: The identification of aged latent fingerprints is often difficult, especially for those of children. To understand this phenomenon,
`the chemical composition of children’s versus adults’ latent fingerprints was examined over time using Fourier transform infrared microscopy.
`Hierarchical cluster analysis revealed that children’s and adults’ prints were distinguishable for up to 4 weeks after deposition, based on differences
`in sebum composition. Specifically, adults had a higher lipid content than children, but both decreased over time, attributable to the volatility of
`free fatty acids. The aliphatic CH3, aliphatic CH2, and carbonyl ester compositions changed differently in adults versus children over time, consis-
`tent with higher cholesterol and cholesteryl esters in children’s prints and wax esters and glycerides in adults’ prints. Thus, fingerprint composition
`changes with time differently in children versus adults, making it a sensitive metric to estimate the age of an individual, especially when the age
`of the print is known.
`
`KEYWORDS: forensic science, latent fingerprints, chemical composition, children, Fourier transform infrared microscopy, hierarchical
`cluster analysis, wax esters, cholesteryl esters, squalene, cholesterol, free fatty acids
`
`Traditional visualization methods of latent fingerprints, such as
`magnetic filings dusting,
`iodine, and cyanoacrylate fuming, are
`widely used in the forensic science field (1). These methods,
`though efficient, inexpensive, and relatively fast, can be limiting to
`an investigation when attempting to preserve valuable trace evi-
`dence found in a latent fingerprint. Thus, efforts are underway to
`find alternative latent
`fingerprint visualization methods, using
`instrumentation that is nondestructive to the fingerprint.
`One particular situation where latent fingerprints are difficult to
`identify is the case of aged prints, especially those of children.
`Several studies have shown that children’s prints often ‘‘disappear’’
`faster than adults’, making them inadequate for lifting after being
`dusted or fumed (2–5). For example, a seminal study using gas
`chromatography–mass spectrometry (GC–MS) showed that chil-
`dren’s fingerprints disappeared faster than adults’ because they con-
`tained more volatile fatty acids (3). In contrast, adults’ fingerprint
`residue contained fatty acid esters, which are higher in molecular
`weight and have low volatility. This investigation spurred a slew of
`later experiments using various instrumentation techniques to inves-
`tigate the chemical composition of latent fingerprints such as
`
`1John Jay College of Criminal Justice, New York, NY.
`2National Synchrotron Light Source, Brookhaven National Laboratory,
`Upton, NY.
`
`3National University, San Diego, CA.
`*This work was funded in part by the US Department of Energy Summer
`Undergraduate Research Internship (SULI) program. The National Synchro-
`tron Light Source is funded by the US Department of Energy under contract
`DE-AC02-98CH10886.
`Received 4 Nov. 2008; and in revised form 2 Jan. 2009; accepted 27 Jan.
`2009.
`
`Ó 2010 American Academy of Forensic Sciences
`
`GC–MS (6–8), ultraviolet fluorescence spectroscopy (9,10), and
`x-ray fluorescence microscopy (11).
`Fourier transform infrared spectroscopy (FTIR) is a noninvasive
`and quantitative technique that has been used to study the composi-
`tion of latent fingerprints based on their unique vibrational spectro-
`scopic signatures. It has been used to determine the lipid composition
`in fingerprint residue (12,13) and as a biometric gauge of an individ-
`ual’s age (14). For the analysis of small and⁄ or heterogeneous
`samples, IR light can be focused through an IR microscope for a
`spatial resolution of a few microns (15). Fingerprints are naturally
`heterogeneous materials, containing small particles of skin, droplets
`of sebum, and sweat residue. Thus, analysis of fingerprint composi-
`tion with an FTIR microscope provides the added advantage of being
`able to examine individual fingerprint components separately. FTIR
`microscopy (FTIRM) has been used to examine fingerprint composi-
`tion on various surfaces (16–18) and for contaminants (19,20).
`In this study, the chemical composition of children’s and adults’
`latent fingerprints was examined over the course of 4 weeks using
`FTIRM and these results were compared with conventional dusting
`methods. The goal of this work was to determine how specific
`components of fingerprint composition (i.e., skin, sebum, sweat)
`change over time in adults versus children, and how these changes
`influence the ability to predict the age of an individual based on
`his⁄ her fingerprint.
`
`Materials and Methods
`
`Sample Preparation
`
`Six father (ages 35–45 years) and son (ages 7–10 years) pairs
`were asked to provide fingerprints for this 4-week study. For each
`
`Reactive Surfaces Ltd. LLP
`Ex. 1030 (Rozzell Attachment K)
`Reactive Surfaces Ltd. LLP v. Toyota Motor Corp.
`IPR2016-01914
`
`513
`
`

`

`514
`
`JOURNAL OF FORENSIC SCIENCES
`
`participant, the hands were first washed with soap and water and
`dried thoroughly. Participants were then asked to touch their face
`with an index finger, and then place that finger onto an infrared-
`reflective (MirrIR) glass microscope slide (Kevley Technologies,
`Chesterland, OH). This procedure was then repeated 10 times,
`where subsequent prints were placed on conventional glass micro-
`scope slides. For each print, the same index finger was used and
`the face was touched between each deposition. A total of eleven
`fingerprints were collected per person (one on a MirrIR slide and
`10 on conventional glass slides). All prints were stored at room
`temperature (22°C) and a relative humidity of 20% for the duration
`of the experiment. Fingerprints were analyzed by dusting and
`FTIRM twice a week for 4 weeks as described below. On week 4,
`the remaining prints were heated for 24 h at 43.3°C. This was done
`in order to test whether changes in temperature affect the latent fin-
`gerprint composition.
`
`Dusting
`
`Twice a week, one fingerprint from each participant was dusted
`using black magnetic fingerprint powder (Lightning Powder Com-
`pany, Salem, OR). The print was lifted with transparent
`tape,
`placed into a notebook, and labeled. After each dusting, the dark-
`ness of the print was scaled by counting the number of distinguish-
`able minutiae that were clearly visible.
`
`FTIR Microscopy
`
`For each participant, the fingerprint that was deposited on the
`infrared-reflective glass slide was analyzed using a Perkin Elmer
`Spectrum Spotlight FTIR Imaging System. For each print, 3–5 skin
`particles and 3–5 sebum droplets were identified and their stage
`coordinates on the FTIR microscope were recorded so that the
`same regions could be analyzed for changes during the course of
`the experiment. Salt deposits from sweat were not probed in this
`study because there were insufficient areas in the children’s
`fingerprints.
`Spectra from skin and sebum areas were collected in transflec-
`tance mode from 4000 to 800 cm)1 using a 25 · 25 lm square
`aperture. For each spectrum, 64 scans were co-added using a spec-
`tral resolution of 4 cm)1.
`
`Data Analysis
`
`After data collection, spectra were exported to Thermo Nicolet
`Omnic Macros Basic for analysis. For each skin spectrum, the pro-
`tein and lipid areas were integrated as shown in Table 1. For the
`sebum spectra, only the lipid areas (full, CH3, and CH2) were cal-
`culated. After integration, a series of ratios were calculated for each
`spectrum: lipid⁄ protein, CH3⁄ lipid, CH2⁄ lipid, and carbonyl ester⁄
`lipid. Ratios were generated in order to normalize to the total pro-
`tein or lipid content. For the fathers and sons at each time point,
`ratios were averaged (mean € SE), and plotted as a function of
`time.
`Hierarchical cluster analysis (HCA) was also performed on the
`averaged spectra at each time point using opus software (Bruker
`Optics, Billerica, MA). All spectra were first vector normalized to
`account for variations in sample thickness. Ward’s algorithm was
`used to calculate the heterogeneity between clusters to generate a
`dendrogram. The heterogeneity between clusters indicates the
`degree of spectral similarity within the given spectral region. Clus-
`ter analysis was performed for the lipid, protein, and carbonyl ester
`regions as listed in Table 1.
`
`TABLE 1—FTIR parameters used to analyze the skin and sebum spectra.
`
`Range (cm)1)
`
`Baseline (cm)1)
`
`2750–3100
`2948–2953
`2918–2928
`1125–1210
`1585–1480
`
`2750–3100
`2750–3100
`2750–3100
`1125–1210
`1585–1480
`
`Region
`
`Lipid
`CH3
`CH2
`Carbonyl ester
`Protein
`
`Results
`
`Fingerprint residue is composed of three main components: skin,
`sebum, and sweat (5). All three components are visibly distinguish-
`able with light microscopy. Moreover, since the chemical makeup
`of these components is different, they each have unique FTIR spec-
`tra, as can be seen in Fig. 1. Skin cells in a fingerprint are those
`sluffed from the outermost epidermis and consist mainly of protein.
`The repeating amide-bond backbone of proteins gives rise to their
`unique FTIR spectra (15). Specifically, the amide I band between
`1700 and 1600 cm)1, arises from the C = O stretching vibration
`of the amide bond. The amide II band (1580–1480 cm)1) is
`assigned to a combination of N-H bending and C-N stretching in
`the amide bond.
`Sebum is an oily substance produced by the sebaceous glands
`and is composed largely of a variety of lipids (21). Sweat found in
`the residue of a fingerprint is secreted by eccrine sweat glands and
`is mainly composed of various organic and inorganic salts (12).
`The sebum spectrum contains characteristic lipid peaks, including
`the large CH3 and CH2 symmetric and antisymmetric peaks from
`3100 to 2700 cm)1 and peaks centered near 1740 and 1180 cm)1
`attributed to the C = O and C-O vibrations from carbonyl esters
`(e.g., wax esters and cholesteryl esters), respectively. Sweat spectra
`can also be identified by the characteristic carboxylic acid peak
`(COOH) from lactic acid between 1500 and 1600 cm)1. The broad
`peak centered around 3300 cm)1 in both the skin and sweat spectra
`arises from hydrogen-bonded OH groups in both proteins and lactic
`acid.
`Since individual peaks in an FTIR spectrum represent different
`chemical components, chemical images can be generated from an
`entire fingerprint. For example, by integrating the protein peak or
`lipid peak, chemical images of the entire fingerprint’s skin (Fig. 2a)
`or sebum (Fig. 2b) were generated, respectively.
`Conventional dusting of the adults’ and children’s fingerprints
`over the 4-week duration of the experiment is shown in Fig. 3. At
`all time points, the fathers’ prints (Fig. 3a) dusted darker than the
`sons’ prints (Fig. 3b). As time progressed,
`the fathers’ prints
`remained visibly unchanged, while the fine minutiae of the sons’
`prints became more difficult to visualize.
`HCA was performed on the time-point-averaged father and son
`spectra in the lipid, protein, and carbonyl ester regions (Fig. 4).
`The resulting dendrograms clearly show two distinct clusters sepa-
`rating the fathers’ and sons’ lipid spectra for both skin (Fig. 4a)
`and sebum (Fig. 4b) regardless of time (i.e., fingerprint age). A
`similar trend was observed for the carbonyl ester dendrogram from
`the sebum spectra (Fig. 4c). The fathers’ and the sons’ spectra did
`not cluster separately in the protein spectral region from the skin
`spectra (Fig. 4d).
`Once it was clear that the fathers’ and sons’ prints were distin-
`guishable through HCA, further analysis was performed to evaluate
`the change in fingerprint composition over
`time and how it
`influenced the ability to distinguish a child’s from an adult’s finger-
`print. Figure 5a shows the lipid⁄ protein peak area ratio as a func-
`tion of time for the fathers versus the sons. As can be seen, the
`
`

`

`ANTOINE ET AL. • TIME DEPENDENCE OF CHILDREN’S AND ADULTS’ LATENT FINGERPRINT COMPOSITION 515
`
`FIG. 1—FTIRM spectra of skin, sebum, and sweat with their corresponding light micrographs. Scale bar: 20 lm.
`
`a
`
`b
`
`FIG. 2—FTIRM images of a child’s fingerprint generated by integrating the (a) protein and (b) lipid spectral regions. Scale bar: 500 lm.
`
`a
`
`b
`
`FIG. 3—Light micrographs of the dusting results over the course of the experiment for the (a) fathers and (b) sons.
`
`fathers had a significantly higher lipid content in the skin than
`the sons at all time points. Over the 4-week duration of this study,
`both the fathers’ and sons’ lipid⁄ protein ratio decreased at a similar
`rate.
`To characterize the type of lipids present in the sebum, the
`CH3 and CH2 peak areas were calculated and normalized to total
`lipid content. Specifically, the relative abundances of short- and
`long-chain lipids, and branched versus straight-chain lipids, were
`evaluated by calculating the CH3⁄ lipid and CH2⁄ lipid peak areas
`as a function of time (Fig. 5b–d). At early time points, the sons
`had a lower CH3⁄ lipid ratio than the fathers (Fig. 5b). However,
`this ratio increased steadily over time for the sons, such that they
`were indistinguishable from the fathers after 4 weeks. For the
`fathers, this ratio remained unchanged over time. For the CH2⁄ li-
`pid ratio,
`the fathers’ values were consistently lower than the
`sons’, and both increased slightly over time (Fig. 5c). Analysis of
`the carbonyl esters showed that the sons and fathers had similar
`values at the start of the experiment (Fig. 5d). However over time,
`
`the amount of carbonyl esters increased in the sons while they
`decreased in the fathers. Thus, after 4 weeks, the sons and fathers
`had significantly different carbonyl ester content in their finger-
`print residue.
`
`Discussion
`
`Sebum is the main oily component of latent fingerprints and it is
`composed mainly of 30% free fatty acids, 33% glycerides, 22%
`wax esters, 10% squalene, and 5% cholesterols and hydrocarbons
`(22). The fingerprint dusting technique relies on the mechanical
`adherence of fingerprint powder to the moisture and sebum compo-
`nents of the skin ridge deposits such that the dusting intensity is
`determined by the moisture and oil concentration of the print donor
`(23). A number of studies have shown that children produce less
`sebum than adults until they reach puberty (24–29) when the seba-
`ceous glands become more active (14). The dusting and FTIRM
`results presented here are consistent with these findings, where the
`
`

`

`516
`
`JOURNAL OF FORENSIC SCIENCES
`
`FIG. 4—HCA for the (a) lipid composition in the skin, (b) lipid composition in the sebum, (c) carbonyl ester composition in the sebum, and (d) protein com-
`position in the skin.
`
`a
`
`c
`
`b
`
`d
`
`FIG. 5—FTIR parameters (mean € SE) for the fathers (-¤-) versus sons (-•-) as a function of time for the (a) lipid ⁄ protein ratio, (b) CH3 ⁄ lipid ratio,
`(c) CH2 ⁄ lipid ratio, and (d) carbonyl ester (CE) ⁄ lipid ratio.
`
`adult prints dusted darker across all time points and the lipid ⁄ pro-
`tein ratio was consistently higher, respectively.
`Not only does sebum concentration change with age in the
`fingerprints, the lipid composition has also been shown to differ
`between adults and children (24,26,27). In this study, we used
`HCA to examine whether these differences could be observed with
`FTIRM. The HCA performed on the lipid and carbonyl ester
`regions demonstrated that
`there was a significant difference
`between adults’ and children’s sebum and skin, especially in the
`lipid and carbonyl ester spectral regions. Similar findings were
`observed using principal components analysis (PCA) recently (14).
`To further understand the specific compositional differences, the
`individual contributions from the CH3 and CH2 groups were exam-
`ined in the FTIRM spectra. For short-chain and⁄ or highly branched
`lipids, the fraction of CH3 groups in the molecule are higher and
`will have a larger contribution to the FTIRM spectrum. Conversely,
`
`long- and⁄ or straight-chain lipids should have a higher fraction of
`CH2 groups in the lipid spectral region.
`In the sebum of postpubertal individuals, more highly branched
`lipids have been observed, consisting of squalene, wax esters, and
`branched fatty acids (14,27). In the FTIRM data,
`these highly
`branched lipids resulted in a higher fraction of CH3 groups and
`lower fraction of CH2 groups in the adult sebum. Conversely, chil-
`dren’s sebum has been shown to have high concentrations of long-
`chain fatty acids, cholesterol, and cholesteryl esters (30,31). Here,
`the children’s prints were found to have a higher fraction of CH2
`groups and a lower fraction of CH3 groups than the adults, consis-
`tent with a greater number of
`straight-chained lipids and
`cholesterol.
`Over time, the lipid concentration and composition changed in
`all fingerprints. The total lipid content decreased in both the fathers
`and sons, which is supported by several chromatography⁄ mass
`
`

`

`ANTOINE ET AL. • TIME DEPENDENCE OF CHILDREN’S AND ADULTS’ LATENT FINGERPRINT COMPOSITION 517
`
`spectrometry studies and attributed to the volatility of low molecu-
`lar weight components (2,3,32,33). These components are most
`likely free fatty acids, which represent 30% of the sebum compo-
`sition (22) and have been shown to be the most volatile compo-
`nents by thin layer chromatography (33). More specifically, the
`free fatty acids are primarily straight-chain aliphatic molecules that
`vary in length, where the shorter chain molecules have the highest
`volatility. The FTIRM data show an increased CH2 fraction over
`time especially in children’s prints, consistent with a disappearance
`of the shorter chain fatty acids and retention of longer fatty acids,
`the latter of which have a higher fraction of CH2 groups per lipid
`molecule.
`There were noticeable compositional differences between the
`fathers’ and sons’ prints over the course of the experiment. For
`example, we found that the fraction of CH3 groups in the children’s
`sebum increased but remained constant in adults. Children’s prints
`have a high concentration of cholesterol, unlike adults (30,31).
`Since cholesterol is not observed in aged prints (33), and its molec-
`ular structure has a low CH3⁄ lipid ratio, we suggest
`that
`the
`increased CH3 fraction in children’s prints over time may arise
`from the disappearance of cholesterol over time. Conversely, adults’
`prints have very little cholesterol, which is consistent with the
`unchanged CH3 fraction over time.
`We find that the carbonyl ester fraction was similar between
`adults and children at the start of the experiment, but became
`increasingly different over the course of 4 weeks. This was likely
`due to different sources of carbonyl esters in adults’ versus chil-
`dren’s prints. Specifically, the carbonyl ester contribution from the
`children’s prints is attributable to a high concentration of cholesteryl
`esters, which are highly stable over time (2,24,28). On the other
`hand, the carbonyl ester contribution in the adults’ prints arises pri-
`marily from wax esters. Wax esters are composed of a wide range
`of esterified fatty acids, making their volatility more variable than
`cholesteryl esters. Since the adults’ carbonyl ester contribution
`decreases over time, these findings suggest the disappearance of
`more volatile wax esters.
`In summary, this study showed that fingerprints change composi-
`tion significantly over time, and these changes are different in chil-
`dren versus adult prints. Specifically, the results indicate that all
`sebum contains a high content of volatile fatty acids that cause fin-
`gerprints to ‘‘disappear’’ over time. However, children’s sebum also
`contains a higher proportion of cholesterol, cholesteryl esters, and
`straight-chain fatty acids that are different in stability from the
`squalene, wax esters, and branched fatty acids contained in adults’
`sebum. Based on these differences, children’s prints can still be dis-
`tinguished from adults’ prints even 4 weeks after deposition. These
`findings support recent work demonstrating the ability to classify
`the age of a person based on the FTIR spectrum of his⁄ her finger-
`print (14), and confirm that this can even be done for aged prints.
`However, care should be taken when gauging the age of an indi-
`vidual through FTIR analysis, where the age of the fingerprint itself
`should first be determined if possible. Thus, FTIRM is a comple-
`mentary tool
`to conventional dusting methods because its non-
`invasive nature makes it useful for preserving trace evidence,
`while the spectral features provide unique information on sebum
`composition.
`
`Acknowledgments
`
`We would like to thank Jaclyn Novatt, Lara Hershcovitch,
`Meghan Ruppel, and Randy Smith for their valuable input and
`assistance. A special
`thanks to the six father–son pairs who
`enthusiastically participated in this experiment.
`
`References
`
`1. Wargacki SP, Lewis LA, Dadmun MD. Understanding the chemistry of
`the development of latent fingerprints by superglue fuming. J Forensic
`Sci 2007;52(5):1057–62.
`2. Noble D. Vanished into thin air. The search for children’s fingerprints.
`Anal Chem 1995;67(13):435A–8A.
`3. Buchanan MV, Asano K, Bohanon A. Chemical characterization of fin-
`gerprints from adults and children. SPIE 1997;2941:89–95.
`4. Blasdell R. The longevity of latent fingerprints of children vs adults.
`Policing: Int J Police Strateg Manage 2001;24(3):363–70.
`5. Ramotowski R. Composition of latent print residue. In: Lee HC, Gaens-
`slen RE, editors. Advances in fingerprint technology. Boca Raton, FL:
`CRC Press, 2001;64–95.
`6. Asano KG, Bayne CK, Horsman KM, Buchanan MV. Chemical compo-
`sition of fingerprints for gender determination. J Forensic Sci 2002;
`47(4):805–7.
`7. Croxton RS, Baron MG, Butler D, Kent T, Sears VG. Development of a
`GC-MS method for the simultaneous analysis of latent fingerprint com-
`ponents. J Forensic Sci 2006;51(6):1329–33.
`8. Richmond-Aylor A, Bell S, Callery P, Morris K. Thermal degradation
`analysis of amino acids in fingerprint residue by pyrolysis GC-MS to
`develop new latent fingerprint developing reagents. J Forensic Sci 2007;
`52(2):380–2.
`9. Jones NE, Davies LM, Brennan JS, Bramble SK. Separation of visibly-
`excited fluorescent components in fingerprint residue by thin-layer chro-
`matography. J Forensic Sci 2000;45(6):1286–93.
`10. Akiba N, Saitoh N, Kuroki K. Fluorescence spectra and images of latent
`fingerprints excited with a tunable laser
`in the ultraviolet
`region.
`J Forensic Sci 2007;52(5):1103–6.
`11. Worley CG, Wiltshire SS, Miller TC, Havrilla GJ, Majidi V. Detection
`of visible and latent fingerprints using micro-X-ray fluorescence elemen-
`tal imaging. J Forensic Sci 2006;51(1):57–63.
`12. Ricci C, Phiriyavityopas P, Curum N, Chan KLA, Jickells S, Kazarian
`SG. Chemical
`imaging of latent fingerprint residues. Appl Spectrosc
`2007;61(5):514–22.
`13. Azizian H, Kramer JKG. A rapid method for the quantification of fatty
`acids in fats and oils with emphasis on trans fatty acids using Fourier
`transform near infrared spectroscopy (FT-NIR). Lipids 2005;40(8):855–
`67.
`14. Hemmila A, McGill J, Ritter D. Fourier transform infrared reflectance
`spectra of latent fingerprints: a biometric gauge for the age of an indi-
`vidual. J Forensic Sci 2008;53(2):369–76.
`15. Humecki HJ. Practical guide to infrared microscopy. New York, NY:
`Marcel Dekker, 1995.
`16. Williams DK, Schwartz RL, Bartick EG. Analysis of latent fingerprint
`deposits by infrared microspectroscopy. Appl Spectrosc 2004;58(3):313–6.
`17. Tahtouh M, Kalman JR, Roux C, Lennard C, Reedy BJ. The detection
`and enhancement of latent fingermarks using infrared chemical imaging.
`J Forensic Sci 2005;50(1):64–72.
`18. Crane NJ, Bartick EG, Perlman RS, Huffman S. Infrared spectroscopic
`imaging for noninvasive detection of latent fingerprints. J Forensic Sc
`2007;52(1):48–53.
`19. Grant A, Wilkinson TJ, Holman DR, Martin MC. Identification of
`recently handled materials by analysis of latent human fingerprints using
`infrared spectromicroscopy. Appl Spectrosc 2005;59(9):1182–7.
`20. Ricci C, Chan KLA, Kazarian SG. Combining the tape-lift method and
`Fourier transform infrared spectroscopic imaging for forensic applica-
`tions. Appl Spectrosc 2006;60(9):1013–21.
`21. Smith KR, Thiboutot DM. Sebaceous gland lipids: friend or foe? J Lipid
`Res 2008;49(2):271–81.
`22. Victoria Police VFSC. Fingerprint branch training manual, module nine,
`latent fingerprint composition. Melbourne, Victoria: Victoria Forensic
`Science Centre, 2002.
`23. Sodhi GS, Kaur J. Powder method for detecting latent fingerprints: a
`review. Forensic Sci Int 2001;120(3):172–6.
`24. Ramasastry P, Downing DT, Pochi PE, Strauss JS. Chemical composi-
`tion of human skin surface lipids from birth to puberty. J Invest Derma-
`tol 1970;54(2):139–44.
`25. Downing DT, Stewart ME, Strauss JS. Changes in sebum secretion and
`the sebaceous gland. Dermatol Clin 1986;4(3):419–23.
`26. Stewart ME, Downing DT. Proportions of various straight and branched
`fatty acid chain types in the sebaceous wax esters of young children.
`J Invest Dermatol 1985;84(6):501–3.
`27. Stewart ME, Steele WA, Downing DT. Changes in the relative amounts
`of endogenous and exogenous fatty acids in sebaceous lipids during
`early adolescence. J Invest Dermatol 1989;92(3):371–8.
`
`

`

`518
`
`JOURNAL OF FORENSIC SCIENCES
`
`28. Yamamoto A, Serizawa S, Ito M, Sato Y. Effect of aging on sebaceous
`gland activity and on the fatty-acid composition of wax esters. J Invest
`Dermatol 1987;89(5):507–12.
`29. Yamamoto A, Serizawa S, Ito M, Sato Y. Fatty acid composition of
`sebum wax esters and urinary androgen level in normal human individu-
`als. J Dermatol Sci 1990;1(4):269–76.
`30. Downing DT, Strauss JS, Norton LA, Pochi PE, Stewart ME. The time
`course of lipid formation in human sebaceous glands. J Invest Dermatol
`1977;69(4):407–12.
`31. Stewart ME, Downing DT. Unusual cholesterol esters in the sebum of
`young children. J Invest Dermatol 1990;95(5):603–6.
`32. Archer NE, Charles Y, Elliott JA, Jickells S. Changes in the lipid com-
`position of latent fingerprint residue with time after deposition on a sur-
`face. Forensic Sci Int 2005;154(2–3):224–39.
`
`33. Olsen RD. Chemical dating techniques for latent fingerprints: a preli-
`minary report. The Print 1995;11(5):1–4.
`
`Additional information and reprint requests:
`Lisa M. Miller, Ph.D.
`National Synchrotron Light Source
`Brookhaven National Laboratory
`75 Brookhaven Avenue
`Upton, NY 11973-5000
`E-mail: lmiller@bnl.gov
`
`