Reactive Surfaces Ltd. LLP
`Ex. 1033 (Rozzell Attachment N)
`Reactive Surfaces Ltd. LLP v. Toyota Motor Corp.
`IPR2016-01914
`
`

`

`Fingerprint Detection
`with Lasers
`
`Second Edition, Revised and Expanded
`
`E. Roland Menzel
`Texas Tech University
`Lubbock, Texas
`
`'
`
`n MARCEL DEKKER, !Ne.
`
`MA a Ct l
`
`o 1. 1t , ea
`
`NEW YORK • BASEL
`
`

`

`- - - - - - --~ -
`
`-
`
`ISBN: 0-3247-1~4-3
`
`This book is printed on acid-free paper.
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`Copyright © 1999 by Marcel Dekker, Inc. All Rights Reser,·ed.
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`
`C urrent printing (last digit):
`IO 9 8 7 6 5 4 3 2 I
`
`PRINTED IN THE UNITED STATES OF AMERICA
`
`

`

`7
`
`Photoluminescence-Based
`Physical Treatments
`
`In the early days of laser fingerprint detection. the focu, .. a., on detecuon ""
`inben,nt fingerprint lumine>Cencc f lJ. although dusttng. ,taining. and chemical
`procedure, were aho con,idered. f'mm a conc-eptual per.apecti,c. the maJOr ,1n11-
`egic, for fingerprint detection by photoluminescence. either by laser or incohcr(cid:173)
`mt h~ht soun:cs. had been delineated by 1980 (2- 7]. Stan111g with the 80,,
`major focu, began to target development of heller chemical fingerprint treat(cid:173)
`ment-, to be dealt with ,n Chapter 8. and treatments for time-resolved imaging.
`discu,sed in Chapter 9. In thi, chapter. phy\lcal method., arc dl\CU\\ed. ,tan mg
`"uh fingerprint detection by inherent fingerprint fluorescence.
`
`INITIAL INVESTIGATIONS [1)
`
`7.1
`h was rccogni,ed in 1976 that fingerprim,. fresh and old. could be detected in
`• rather gener-•I "'ay. on a nmge of surface,, thus rendeting the photolumiae,(cid:173)
`cencc approach a potentinlly genernl one. Thus. the initial in,c,tigauon con\ld(cid:173)
`cred a range of aspects of the general approach. which arc enumerated in this
`..:."lion. Detail, y.'ill be taken up in the penonent ~ubsequent section<.
`Fingerprint fluorescence. Tbc is~ue of wbetber the obsened inbettnt
`fingerprint fluorescence i.:. indeed inherent or a ,natter of contrunination of fin(cid:173)
`m, hy lluorescent materinl "'a, iaken up.
`Spectroscopy of fingerprint residue. A fairly "tensi,c study .. a., nee(cid:173)
`"'""> fmm the ooL..et for the best choice of excitmion source and filter ,election
`for fingerprint luminescence observation and photogr-Jph).
`
`155
`
`'
`
`

`

`156
`
`Chapter 7
`
`Conditions under which fingerprints could be detected. Here, a range
`of surface types were examined and potential fingerprint age limitations were
`investigated. Also, issues of compatibility with !he then conventional fingerprint
`detection procedures were addressed.
`Excitation sources. A comparison was made of laser versus incoherent
`light sources, 1he lauer these days being referred to as altemative light sourtes.
`Although filters have improved since 1976. the then staled conclusion that the
`altemative light sources. though portable, would be an order of magnitude less
`sensitive than the large Ar-lasers remains valid today.
`Fingerprint treatments. Early on it was realized !hat background fllJ(),
`rescence would make il necessary 10 devise lingerprim n·ealments that would
`lead 10 more intense fingerprint luminescence or luminescence of a color differ,
`em from lhal of the background, 10 permit optical filtering for background sup,
`pression. The focus then was on dye staining. Today, such srnining after cyano(cid:173)
`acrylate fuming is a bread-and-butter photoluminescence detection procedure
`By 1980, dusting powders and chemical 1rea1menls had been devised. However.
`lhe chemical treatments were no1 comparable in sensitivity to those 1ha1 would
`follow later.
`Fingerprint phosphorescence. Here, the recognition that fingerprint
`development would allow suppression of background fluorescence (lhe time·
`resolved approach) pertains. By 1979, the feasibility of this strategy had been
`demonstrated but it would take another 15 years to bring the approach 10 matu,
`rity from the inslrumenlaliod perspective. From a chemistry perspective, lime·
`resolved imaging is not truly mature even today. However, there are sel'eral
`procedures that have reached lhe maturity required for operational implementa·
`tion. These will be taken up in Chapter 9.
`Fingerprint age determination. The potential of determining finger·
`print age by phololuminescence technique., was envisioned early on. A compre·
`hcnsive study involving inherent lingerprilll fluorescence would be undenaken
`in the early 80s, ,vith no success. This is an important area that remains eJusnt
`even lc)day.
`
`7.2
`
`I
`INHERENT FINGERPRINT FLUORESCENCE
`
`A material, in order to yield photoluminescence, must first absorb the incidelll
`luminescence excitation light. Thus, we exantlne lhe absorption of fingerpnr1
`residue. sketched in Fig. 7.1. Nol surprisingly, lingerprinl residue absorbs be~
`in the deep ultraviolet. corresponding 10 absorption by relatively small organic
`molecules. As pointed out in Pan I of this volume, !here are no lasers operatin,
`in !his range lhal are of practical use in a law enforcemem fingerprint idenlifica·
`Lion section. UV lamps are nol sufficiently imense eilher. Fortunately. there i,
`(albeit weak) absorption in the blue-green, leading 10 fluorescence. This prompl·
`
`C " C
`" i:!
`
`C .. .c ..
`
`Fu
`
`ed
`fir
`ra,
`nu
`ex
`wi
`ex,
`va
`45
`60
`wa
`ri7
`
`fin
`nu
`n1a
`un,
`res
`ten
`an,
`by
`of
`po~
`
`

`

`Chapter 7
`
`Photoluminescence-Based Physical Treatments
`
`157
`
`:ou/d be detected. Here, a range
`,I fingerprint age limitations were
`h the then conventional fingerprint
`
`as made of laser versus incoherent
`-red lO as alternative light sources.
`:he then stated conclusion 1ha1 I/le
`,uld be an order of magnitude less
`id 1oday.
`NOS realized that background fluo(cid:173)
`fingerprinl 1rea1ments that would
`, or luminescence of a color differ(cid:173)
`Kical tillering for background sup(cid:173)
`. Today, such staining after cyano(cid:173)
`.urninescence detection procedure.
`men1s had been devised. However.
`, in sensitivity to those that would
`
`e, the recognition that fingerprinl
`,ckground fluorescence (the 1ime(cid:173)
`"'sibili1y of this strategy had been
`"'' 10 bring the approach to matu•
`01n a chemistry perspccti ve, time(cid:173)
`today. Howevcr1 lhere are several
`iuired for operaiional implemcn1a-
`
`e potential of de1ermining finger·
`1as envisioned early on. A compre(cid:173)
`fluoresccnce would be undertaken
`1nporta.Qt area that remains elusive
`
`lORESCENCE
`
`nee, must first absorb the incident
`mine the absorption of fingerprint
`ly. fingerprint residue absorbs best
`orprion by relatively small organic
`,lume, there are no lasers operating
`enforcement fingerprint identifica(cid:173)
`intense either. Fortunately, there is
`iding 10 tluorescence. This prompl-
`
`1 I
`\
`\
`\
`.....,
`\ A
`
`u
`C
`
`•
`• -e
`l:0.5
`i
`
`200
`
`X 10
`
`\
`\
`\
`\
`
`300
`
`400
`
`600
`
`wavelength (nm)
`
`FIGURE 7.1 Absorption of fingerprint residue.
`
`ed !he initial choice of the Ar-laser for fingerprint work. Fluorescence spectra of
`fingerprint residue-to determine what fluorescence exisL~ in the visible spectral
`range, as necessary for visual observatiot and subsequent photogrnphy-reveal
`fluorescence.~ al about 470, 500, and 550 nm. The 1wo former emissions require
`excitation in !he deep blue 10 UV range. but are very weak under exci1ation
`with available ligh1 sources. The emission a1 550 nm is best matched wi1h green
`excitation (see Fig. 9 of ref. I), nicely compatible with Ar-lasers and also copper
`vapor lasers and, under this color of exciiation, is rather more intense than the
`450 and 500 nm emissions. It is a broad emission tailing into the red, beyond
`600 nm, with a St0kes shift amply large to allow the use of ordinary long(cid:173)
`wa,·elength•pass filters. The exciiation/emission/filtering situation is summa(cid:173)
`rized in the ske1ch oF Fig. 7.2.
`Even though precautions had been take in the original srudy of inherent
`fingerprint fluorescence detection, by washing hands. to ensure that the observed
`lluoreseence was not a matter of contamination of fingers by foreign fluorescent
`material, a controversy soon arose as to the nature of the fluorescence observed
`under laser of untreated fingerprints. Carey (8) claimed that all fingerprint tlu<>(cid:173)
`rescence \vas due to contaminatjon. Men1..el and Duff took issue "'ilh this con(cid:173)
`tention [9]. pointing out that Carey himself reported fluorescence from untreated
`and uncontaminated fingerprints. The controversy was revived two years later
`by Salares et al. (!OJ. They expressed surprise, incidentally, that fluorescence
`of fingerprints deposited on glas.~ showed weaker fluorescence than prints de(cid:173)
`posited on paper. TI1ey should 1101 have been. Incident Jigh1 on gla.~s must di-
`
`

`

`158
`
`C
`
`:,
`
`'ii'
`"' C
`,e
`-,;
`•
`• -.E
`•
`u
`• u
`C
`• • C
`·e
`.a
`
`10
`
`8
`
`6
`
`4
`
`2
`
`514.5 nm
`
`line
`
`Ar-laser ~
`I
`I
`I
`I
`
`300
`
`400
`
`600
`
`600
`
`700
`
`wavelength (nm)
`
`FIGURE 7.2 Spectral summary of inherent fingerprint fluorescence detection.
`'
`
`rec1ly hit fingerprint residue lO cause it 10 fluoresce. On substrates that scauet.
`such as paper and styrofoam. for instance. light scattered within the substrate
`can reach the fingerprint deposit (indirect hiLs) 10 cause additional Ouore.scenct
`by the fingerprint. Today, the laser examination of fingerprints on transparen1
`substrates is known to benefit from putting below the substrate another substrate
`that scatters light effectively (without producing background fluorescence).
`It has ~ recognized for many years that palmar perspiration i, largely
`caused by fright. anger. excitation. etc .. rather than physical exertion. Thu~
`when li1nited nu1nbers of articles are exa1nined. one 1nust .. to arrive at a tenable
`conclusion, pay attention to the mental state of the individual depositing fingtr·
`prints. Indeed. the early results obtained with ninbydrin were quite disappoin1ing
`because this aspect of fingerprint deposition was not accounted for sufficient!)
`In any event. the controversy was not long-lived. Inherenc fingerprint fluore~
`cence was rather persuasively demonstrated by Willinski [ 11 ), who investigated
`the permeation of palmar perspiration through laboratory gloves. His intete11
`was in connection with the op1ics industry. Optical surfaces are often coaloo
`(e.g., anti-reflection coatings). Contaminalion of the optical surface inhibiL, tht
`deposition of the coating or causes the coating to lack durability. Thus, cleanl ·
`ness, as in the semiconductor industry, is a major issue. Willinski had his sub,
`
`Chapter 7
`
`Photolur.
`
`,-- 100
`
`50
`
`'I-
`~
`:,
`!"
`
`jeers clea
`care that
`Gloved r,
`variation
`gerprinl r
`cence. Wi
`cenain g l
`classificac
`about 18(
`qualily 11
`years. So,
`situatjon
`prints are
`easily det.c
`fingerprin
`is aggrava
`Bee:
`fingerprin1
`items coll
`,uccessful
`of cases i
`with great,
`print units
`considered
`taining ide
`that this ,.
`idemificati
`correspond
`20% 115].
`and that d,
`cyanoacryl
`du res-we:
`care v.rith \
`Here. laser
`cited nu1nt
`(Vletropolit
`" i 11 deal "
`pact fingeri
`
`7.2.1 Fi1
`
`Ahhough n
`con1ponent~
`
`

`

`Chapter 7
`
`Photoluminescence-Based Physical Treatments
`
`159
`
`- - 100
`
`)
`
`700
`
`rpont fl00<escenc:e detection.
`
`esce. On substrate, that ,caucr.
`t ,cmtered within the substrate
`o c-au" addiuonal fluore,ccnce
`1 of fingerprinL~ on tran,parent
`, the ,ubstrate another substr.1tc
`b.icki;round tluoresccnce).
`.t palnlUf per;piration i5 largely
`than physical e,eruon. n,us.
`ooc mu~t. to am,e at a tenable
`ti., inJ1,idual depositing fmger
`b}<ltill were quite disap(l<>intiog
`not accounted for ,ufficicntly
`d. Inherent fingerprint fluore,
`.,mn,ki I 11 J, "ho an, e,tigate,1
`laboratOf} glo,e,. His 1otcre,t
`1ical ,urfacc, are ofLen co,:~teJ
`the opucal surface inhibit, th'
`1 lack durability. Tims. cleanl1·
`,r i,,uc. Wilhn,ki had his suh
`
`JCCL\ clean their hands via surgical scrub, and then don laboratory gloves. taking
`care tha1 the gloves would not come in contact "ith potential con1am1nant,.
`Glmed fingers were subsequently pressed against clean optical subsll"Jtes. "ith
`, ariation in elapsed time and nature of the u1ili1ed glove. The detection of fin.
`jlerprint material on the optical ,mf.tces touched ul I lizcd laser-excited fluores(cid:173)
`c-ence. WiUinski reponed not only the permeation of fingerpnnt ma1crinl through
`cennin glove types, but even the detection of fingerprint detail sufficient for
`cla,,<ification. English investigators have reported in 1984 that over 4W of
`,bout 180 individuals tested ga,e naturally Ouorcscem fingerprint, of good
`quality [12J. This figure" 1n keeping with the author's experience over the
`yem. Some individuals are good fingerprint donors, others are not. A ,imi lnr
`"tunt1on pcnains quite genernUy. For inswncc, there are indh ,duals whose
`prints are readily developed by ninhydrin and othe" whose fingerprint, are not
`e .. ,ily detected (secretors ,er;us non,ecrcto,·s) by this procedure. ,omething the
`liDj;erprint communuy ha< been aware of for innumeruble years. TI,e situation
`" aggrnvated by the abo,e-menuoncd ··adrenahne' fac1or.
`Because of the difficulty of controlling the many variable, involved in
`fingerpnnt deposition, the only imporwnt tursey, invohe large numbers of
`nem, collected in actual criininal ca,e work. Jn actual case '-"Ork. Creer was
`'IIC\:essful "ith laser detccuon by inherent fingerprint fluorescence in some 30<J(cid:173)
`of cn.•a" invohing polyethylene bag< (13]. TI,c examination wa~ carried out
`with greater care. I note. than what typically is done in case work in most latent
`print units. In nn early i.urvey of nearly 400 anicle,, of ,ariou, t)pe,,, mo,t
`ro1>-1dcred unsuitable for trea1rnent by conventional mean,, Creer reported ob·
`.ainmg identifiable fingerprint, on abou1 30% of them [141. It should be n()(ed
`1bat tbi, work was performed in England. where 16 points are required for
`1dentificotion, a number lnrger than what typically ,s needed m the U.S. The
`corresponding rme for fi later. larger. sample of o,er 3000 anicles \\OS about
`))' (15[. Thi, is gocld ,uccess, considering the range of surfa<XS examined
`....i that dusting "1th nuorescent powder . .iaining with Ouorescent dye (after
`qanoacrylate fuming). and mnh)drinl£inc chloride-all highly effective proce(cid:173)
`dun,,-werc not involved in the abo,e e,amination,. I emphMizc here that the
`care "11h which lhe evidence exa,nination i, conducted detennine"' it, succe~s.
`Here. l.,ser detection 1s less forgiving than du,ting, for instance. The abo,e-
`• t«I number.. are a te,timony to th~ quality of the work conducted by Creer
`~l•tropotitan Police Forensic Science l-1boratory, London). In Chapter 9, we
`•ill deal with optimization of e,eitation, filter;, etc., maucrs that strongly irn·
`pact fin~erprint dctcctubility .
`
`7.2.1 Fingerprint Composition
`
`~l~1ough no comprehensi.e worl to date has been performed to identify the
`tt>mponent, in fingerpriot residue that are responsible for the ob,ervcd finger-
`
`

`

`160
`
`Chapter 7
`
`Photolumlm
`
`print luminescence, some work has been done on chromatographic separation
`of fingerprint material. Early studies along this line [3]. with ether as the mobile
`phase in thin-layer chromatography (TLC), revealed six luminescent bands un(cid:173)
`der blue-green Ar-laser light. On laser examination of TLC plates that had been
`irradiated by ultraviolet light, additional luminescent bands emerged. The <--Ollec(cid:173)
`tion of fingerprint material involved swabbing fingers with conon swabs soaked
`in ether and extracting the coUected residue in ether solution. Ether was chosen
`because of its volatility, to minimize extraction from the skin of components
`that would otherwise not be found in fingerprint residue. Luminescence speclr.!I
`comparison of the strongest TLC feature. a yellow band al the origin, with a
`vitamin B tablet. under 488 and 514.S nm laser excitation, suggested that this
`feature is due to riboflavin [3 J. Later work by the author (unpublished), involv(cid:173)
`ing riboflavin powder and TLC of fingerprint residue. and also excitation spec(cid:173)
`tra. supports this suggestion. Otherwise, identification of the luminescent TLC
`bands reported in reference 13] has not been anempted to date. Only lately bas
`the issue of fingerprint composition seen renewed interest. Bramble performed
`TLC on actual fingerprints to examine the lipid and nitrogenous constituents of
`fingerprints ( 16]. This study is particularly noteworthy in that it represents a
`rnther more realistic approach to idemification of the composition of fingerprints
`than studies involving swabbing with solvents or extraction of components di·
`rectly from the skin via solvents, any number of which have been conducted
`over the years. at times using ultraviolet excitation ror fluorescence examination
`of chromatography bands [3.17-21].
`The subject of fingerprint composition. with particular emphasis on the
`differences between fingerprints of children and adults, was recently investi(cid:173)
`gated by Buchanan et al. [22], using gas chromatography/mass spectroscop).
`The authors raise the interesting prospect of identification of personal tr.lit,
`(gender. habiL~. diseases, etc.) through the examination of fingerprint residue. In
`this connection, note also the recent report on ONA profiling of fingcrprin1
`residue (23]. The subject of TLC study of fingerprint composition will be tal<en
`up further in Chapter IO in connection with rare earth-based fingerprint dctoc-
`tion.
`
`I
`7.2.2 Fingerprint Age Determination
`It would be valuable indeed to the criminalist 10 be able not only to establish
`the idemity of the individual who placed the detected fingerprint but also to I,:
`able to determine when the fingerprint was deposited. The earlier-mentioned
`TLC work of Duff and Menzel (3] was. in fact, aimed at this prospect. Th:
`subject was again taken up by the author in 1980 under a three-year grant from
`the National Science Foundation. This attempt ultimately failed and thus wa;
`not published, other than in the final report on the grant m the NSF and a recem
`
`lener to the,
`The impetus
`show a greer
`orange fluon
`this cc)nnecti
`luminescenct
`lion of lumir
`Thus, once a
`nation prior ·
`The at
`slides by ma
`ccncc spcCll'l
`deposited by
`and also ovc
`7.3 was cont
`also for the s
`cnt occasion~
`capability wi
`as 'l.vell.
`In ligh1
`larly referen
`
`~
`
`1!l ·e
`:;:,
`e
`"'
`
`(/)
`C
`Q)
`1:
`...:
`0 :;:,
`""
`
`3
`
`2
`
`1
`
`FIGURE 7.3
`
`

`

`Chap ter 7
`
`Photoluminescence-Based Physical Treatments
`
`161
`
`lone on chromatographic separation
`his line (3). with ether as the mobile
`revealed six luminescent bands un-
`1ination of TLC plates that had been
`.ineseent bands emerged. The collec(cid:173)
`ng fingers with cotton swabs soaked
`in ether solution. Ether was chosen
`. ction from the skin of components
`Jrint residue. Luminescence spectral
`1 yellow band at the origin, with a
`laser excitation. suggested thal'this
`l>y the author (unpublished), involv(cid:173)
`nt residue. and also excitation spec(cid:173)
`:ntification of the luminescent TLC
`11 attempted to date. Only lately has
`·newed interest. Bramble performed
`ipid and nitrogenous constituents of
`· noteworthy in that it represents a
`ln of the composition of fingerprints
`nts or extraction of components di(cid:173)
`ber of which have been conducted
`itation for nuorescence exanlination
`
`,n, with particular emphasis on the
`n and adulls, was recently investi(cid:173)
`:hromatography/mass spectroscopy.
`of identification of personal traits
`,amination of fingerprint residue. In
`1 on DNA profiling of fingerprint
`ngerprint composition will be taken
`1 rare earth-based fingerprint detec-
`
`Ion
`
`'
`
`list to be able not only to establish
`, detected fingerprint but also to be
`s deposited. The earlier-mentioned
`, fact, aimed at this p011spect. The
`1980 under a three-year grant from
`mpt ultimately failed and thus was
`m the grant to the NSF and a recent
`
`letter to the editor (231. Thus, the essence of the study is briefly discussed here.
`The impetus for the study came from the observation that fresh fingerprints
`show a greenish-yellow fluorescence whereas old fingerprints tend t<> display an
`orange fluorescence. as shown in the spectra of Fig. 7.3. It should be noted in
`this connection that prolonged exposure of fingerprints to light lhat excites the
`luminescence causes spectral changes as well, including (via photodecomposi(cid:173)
`tion of luminescent constituents) a fading of fingerprint luminescence intensity .
`'nius. once a fingerprint is detected by its photoluminescence, prolonged illumi(cid:173)
`nation prior to photography or other recording is to be avoided.
`The above study utilized fingerp,ints deposited unto clean microscope
`slide.~ by many individuals. These fingerprints were then subjected to fluores(cid:173)
`cence spectroscopy over times spanning nearly three years. Also, fingerprints
`deposited by the same individual on different dates were examined while fresh,
`and also over a period of aging time. While the general trend depicced in Fig.
`7.3 ,vas confinned, there were considerable variations behveen individuals and
`also for the spectra of fingerprints from any given individual deposited on differ(cid:173)
`ent occasions, che latter differences likely being (>f dietary origin. No firm dating
`capability was thus obtained. The problem is aggravaced by finger conrnmination
`as well.
`In light of che recent studies of fingerprint composition (note here particu(cid:173)
`larly references 16. 18, and 22), the very imporrnnt topic of fingerprint age
`
`'
`
`:ei' ·c
`:,
`.ri L
`~
`ui
`C
`«> :s
`..:
`0
`:,
`.:
`
`3
`
`2
`
`1
`
`540
`
`580
`
`620
`
`wavelenglll (nm)
`
`FIGURE 7.3 Fluorescence spectra of fresh and old fingerprints.
`
`

`

`162
`
`Chapter 7
`
`Photolur
`
`should be exan1incd again. in a more co1nprehensive v.1ay rhan in Lhe fev.1 and
`sporadic studies of the past, which no doubt were conducted with rather limited
`support (the study of reference 18, for instance. is of a feasibility nature only).
`
`7.3 STAINING WITH FLUORESCENT DYE
`Since the inherent fluorescence of latent fingerprints is generally weak, finger·
`print treaunents have over the years been devised to increase the luminesce~
`intensity, and also 10 vary the color for optical filtering purposes. An early
`procedure involved dipping anicles in a solution of tluorescent dye, or spl'aying
`the solution onto the anicle. The objective would be for the dye to preferentially
`adhere to the fingerprint, to render it visible under subsequent fluorescence exci(cid:173)
`tation. The earliest success was obtained with the dye coumarin 611 1. However.
`the success was not uniform. because the application of the solution tended to
`wash away the fingerprint itself, or, at least. tended to smudge fingerprint detail.
`Also. of course. thel'e was the matter of background staining. The siaining ap·
`proach came into its own. though, upon the advent of the cyanoacrylatc fuming
`procedure. For staining purposes, it is not necessary that the cyanoacrylate fum•
`ing be such that visible (white) fingerprints are developed. Rather, the e,sence
`is that the fonned polymer stabili1.c-s the print, such that it becomes impel'viou<
`to the solvent via \Yhich the staining is done. This is an easily met requirement:
`in many laboratories, Lhe cyanoacrylatc fuming chan1ber is an aquariurn. Thi1;
`allows one to look inside, to moni!Or the fuming. Often, a test item is placed
`into the aquarium together with the evidence, such as a piece of tin foil holding
`a test print. Once that test print is adequately developed. the fuming is stopped.
`Otherwise, t()() much background development is likely to occur. to the detri·
`ment of fingerprint detection. Indeed, the glass of the aquarium eventually be·
`comes white, Lhus preventing viewing of \Yhat goes on inside. The cleaning of
`the glass, to remove the deposited cyanoacrylate polymer, requires an aggressi1·e
`solvent (typically, acetone) for cleaning. Milder solvents, such as the methanol
`often used in dye staining, will not dissolve the polymer. The cyanoacrylme
`polymer fingerprint development has the additional virtue of forming a fine
`substrate for preferential dye adherence, presumably because dye molecules get
`stuck in voids bet,vccn poly1ner chains, in 1nuch the same way in ,vhich molecu·
`Jar sieves function. With the advent of cyanoacrylate fuming, a vast range of
`suitable dyes materialized. On of the be.,t, first shown to be effective by 1980
`[241, and still today the workhorse of post-cyanoacrylate staining in concen
`with luminescence detection, is rhodamine 6G (25), for three reasons. f ic,t. 11
`adheres nicely to the cyanoacrylate polymel'. Second, it has a very high fluores(cid:173)
`cence efficiency. It is. after all, a laser dye. Third, its absorption is beautifull)
`compatible with the Ar-laser, the copper vapor laser. the alternative light ,ouroes
`(when operated in the blue-green), and even the frequency-doubled Nd:YAG
`
`laser. Rh
`well-suit<
`violet (ur
`on adhes:
`tation of
`cessful a
`filtering,
`proach,c
`ity. Then
`Thus, \V(
`namely c
`
`7.3.1
`
`Typically
`of eviden
`illurninat,
`choice of
`ably vola
`times the
`then dil ut
`because,
`a carrier
`used for
`111olar ran
`article v.-i
`to reduce
`concentra
`ing a,vay
`vents. wt
`well. Thi•
`tinely util
`
`7.3.2
`
`C
`'
`There are
`utili 1es ,v
`tory glov.
`gloves is.
`invc.stigat(cid:173)
`tion is ge
`even if in
`scrutiny.
`
`

`

`•
`
`Chapter 7
`
`Photoluminescence-Based Physical Treatments
`
`163
`
`rehensive \Vay than in the fe\v and
`were conducted with rather limited
`,ce. is of a feasibility nature only).
`
`NT DYE
`
`~crprints is generaJly \.veak. linger(cid:173)
`vised to increase the luminesce,Qcc
`>lical filtering purposes. An early
`ion of fluorescent dye, or spraying
`,uld be for the dye to preferentially
`nder :;ubsequcnt fluorescence exci(cid:173)
`the dye coumarin 6 [I]. However.
`plication of the solution tended to
`,nded to smudge fingerprint detai l.
`,ground staining. The staining ap(cid:173)
`d\·ent of the cyan~1crylate fluning
`essary that the cyanoacrylate fum(cid:173)
`,re developed. Rather, the essence
`. such that it becomes impervious
`This is an easily met requirement:
`ng chamber is an aqua.rium. This
`ning. Olten, a test item is placed
`such as a piece of tin foil holding
`developed, the fuming is stopped.
`11 is likely to occur, to the detri(cid:173)
`;s of the aquarium eventually be(cid:173)
`t goes on inside. The cleaning of
`te polymer, requires an aggressive
`er solvents, such as the methanol
`the polymer. The cyanoacrylate
`litional ' virtue or fonning a fine
`mably because dye molecu les get
`h the same way in which molecu(cid:173)
`~crylate fuming, a vast range of
`;t shown to be effective by 1980
`yanoacrylate staining in concert
`; 125], for three reasons. First, it
`econd, it has a very high fluores(cid:173)
`hird, its absorption is beautifully
`laser, the alternative light sources
`the frequency-doubled Nd: Y AG
`
`laser. Rhodamine B, which is very similar in performance to rhodamine 6G. is
`well-suited to the Nd:YAG laser. Luminescence can be obtained from crystal
`violet (under dye laser excitation), which is often used for fingerprint detection
`on adhesive tapes. A similar dye, rosaniline chloride, is amenable co green exci(cid:173)
`tation of nuorescence. DODC. DCM [26] and many other laser dyes are suc(cid:173)
`cessful as well. Finally, mixtures of dyes can be employed, such that optical
`filtering can be implemented for background suppression, with one staining ap(cid:173)
`proach, even when there is considerable background fluorescence color variabil(cid:173)
`ity. There licerally are hundreds of potentially useful fingerprint staining dyes.
`Thus, we C<.>nfine <.>ur detailed discussion to the two early representatives.
`namely coumarin 6 and rhodamine 60.
`
`7.3.1 Dye Solutions
`
`Typically, the staining dye is dissolved in methanol. The treatmenc of the article
`of evidence then proceeds by dipping or spraying. The article. once dry, is then
`illuminated and viewed in the usual way to observe fluorescent fingerprints. The
`choice of methanol is not essential. It is convenient simply because it is reason(cid:173)
`ably volatile, so that articles dry rapidly. For processing adhesive tapes, some(cid:173)
`times the dye is dissolved in alcohol (methanol or ethanol) and the solution is
`then dilmcd with water 127). The initial dissolution in the alcohol is performed
`because water is often only a poor solvent for the dye. The water thus serves as
`a carrier for the solvent only. In the authbr's laboratory, methanol solutions are
`used for adhesive tape processing. Dye concentrations are in the JO-' to IO '
`molar r.tnge. With these concentrations, it is generally not necessary to rin.sc the
`article with a neat solvent after the staining. namely the methanol or ethanol,
`to reduce background staining. This rinsing is often nece.,sary when high dye
`concentrations are used> but is gcneraJJy to be avoided because one risks \\1ash(cid:173)
`ing a\vay fingerprint detail. lvforeover. the rinsing step am(>unts to ,vasting sol(cid:173)
`vents. which arc, these days, becoming expensive. Waste of dye pertains as
`well. This point is raised because all too many Jaw enforcement agencies l'OU·
`finely utilize high dye concentrations, with mandatory post-staining rinses.
`/
`
`7.3.2 Safety
`
`There are certain cornmon and routjnc safety precautions a fingerprint exa.rniner
`utilizes when working with solutions, the most obvious being the use of labora(cid:173)
`tory gl<>ves. to prevent contact between the solution and the skin. The use of
`glo,•es is. in any event. advised to prevent the deposition on the evidence of the
`investigator's fingerprints. which would, at least. be embarrasing. This precau(cid:173)
`tion is generally sufticient for the safe utilization of dye staining procedures,
`even if in the early days of rhodamine 60 staining the dye came under safety
`sc111tiny. Hoopla wa., made of the potential carcinogenic nature of the dye.
`
`

`

`164
`
`Chapter 7
`
`Photo/um
`
`which (28] is reported to become dangerous at a dosage of 1 g/year/10 kg of
`body weight for ingestion or absorption through the skin. This is a dosage that
`far exceeds anything a lat.ent print examiner would conceivably be exposed to:
`in a liter of solvent, a 10-• molar dye concentration amounts 10 the presence of
`only milligrams of the dye. Thus. an examiner would have to literally drink
`liters of the stuff daily. Of course. with methanol as the solvent, such an exam(cid:173)
`iner would go blind. and even die, within a day. As with all fingerprint treat(cid:173)
`ments, it is necessary to maintain a proper perspective. As an aside, similar
`considerations apply to cyanoacrylate fuming. This substance was at one time
`used on the battlefield for the treatment of casualties (it seals wounds rather
`quicky), but this use was, as I understand it. discontinued because of the poten,
`tial carcinogenic nature of cyanoacrylate esters, which would emerge years later
`as a problem. As a battle casualty, in iminent danger of death, I, personally,
`would prefer to survive now than worry about a cancer fourty years after having
`perished in the field.
`
`7.4 DUSTING WITH LUMINESCENT POWDER
`
`Luminc.went dusting powders were available commercially to fingerprint exam(cid:173)
`iners before the advent of laser fingerprint detection in 1976. Their use involved
`ultraviolet lamps for luminc.wence excitation. The conunercially available lamps
`of this kind are of low intensity. Thus, the then available luminescent powders
`were utilized only in special instances, such as the detection of fingerprints on
`highly patterned surfaces. The use of such powders. even in this special situa(cid:173)
`tion, never caught on, though, and certa