Two-Step Matrix Application for the Enhancement and Imaging of

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Two-Step Matrix Application for the Enhancement and Imaging of Latent Fingermarks L. Ferguson, R. Bradshaw, R. Wolstenholme, M. Clench, and S. Francese* Biomedical Research Centre, Sheffield Hallam University, Howard Street S1 1WB, Sheffield, United Kingdom

bS Supporting Information ABSTRACT: Matrix deposition is a crucial aspect for successful matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI MSI) analysis. The search for more efficient protocols over the years has resulted in the devising of “dry matrix methods” in which the matrix is solely or preliminarily deposited as powder and acts in most cases as a seeding agent. Although not fully embraced by the MALDI MSI community, these methods have proven to be more efficient in terms of ion intensity, ion abundance, and ion images in the experimental circumstances they were employed. Here we report a novel two-step matrix application method, that we have named the “dry
wet” method, where the matrix is dusted onto the sample followed by solvent spray using a robotic device. The new method has been successfully applied to the detection and mapping of several analyte classes within latent fingermarks. Dusting the matrix generated the added advantage of enhancing the latent fingermarks which are invisible. This allows not only for an optical image to be taken of the fingermark in situ but also bridges the gap in the application of MALDI MSI technology in this field; with the use of the methodology reported, fingermark enhancement, recovery, and analysis from different surfaces is now compatible with subsequent MALDI MSI analysis thus allowing visual and chemical information to be obtained simultaneously.

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atrix deposition is a crucial aspect in matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI MSI). Extensive research has been undertaken over the years to improve this preparation step with the aim of minimizing analyte delocalization while maximizing the available resolution and analyte extraction from the tissue section. The selection of the most appropriate matrix and solvent combination impacts on the analyte extraction (sensitivity); once the selection of the matrix and solvent combination has been optimized, the image resolution (within the instrumental constraints) and analyte extraction heavily rely on the choice and optimization of the deposition method. Minimization of analyte delocalization can be achieved not only by using appropriate sample pretreatments but also by selecting a deposition method which either confines the matrix to a very small area (microspotting, for example) or spraying the matrix either robotically or manually. Contactless microspotting can currently be achieved by piezo-dispensing the solution using a chemical inkjet printer1,2 or through acoustic ejection first introduced as a prototype by Aerni et al.3 and then improved and commercialized by Labcyte.4 Here both matrix concentration and solvents used to dissolve the matrix have an important role in determining the size of the crystallized droplet and the spotto-spot distance, which determine the final image resolution. Pneumatically assisted matrix spray-coating, for which the first example was reported by Caprioli et al.,5 requires the optimization of the distance between the sample and the spray nozzle, deposition speed, and number of layers (this generally depends on matrix solvent combinations). r 2011 American Chemical Society

The matrix can also be applied through a matrix aerosol created by vibrational vaporization. A number of parameters need to be monitored and optimized such as deposition time, intervals, matrix layer thickness, wetness, and drying rate. This deposition system is claimed to generate a droplet size of 20 μm in diameter typically covering an area on the tissue smaller than 50 μm in diameter. This and the ability to control the relevant deposition parameters have been demonstrated to allow images with excellent spatial resolution and high ion intensity to be achieved.6 For manual spray-coating, it is important to find optimal conditions for the spray distance, number of cycles, and elapsed time between consecutive spraying. Whichever the deposition method, it has an influence on the crystal formation in terms of speed (slow formation has been observed to yield higher intensity signal) and size, with the latter having a direct effect on the image resolution that will then only be limited by the laser spot diameter if oversampling is not performed. The deposition method can also have an effect on the signal intensity as it can impact on the analyte extraction and analyte
matrix cocrystallization. In terms of sample pretreatment, when performing imaging experiments targeting proteins, immersion techniques involving dipping the mounted section in a bath of matrix solution prior to matrix deposition have been observed to increase the signal without delocalizing the analyte.7,8 Independently from the mode of application, the most widely used deposition methods involve the use of “wet” matrix, i.e., Received: March 9, 2011 Accepted: May 27, 2011 Published: June 13, 2011 5585

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Analytical Chemistry dissolved in an appropriate solvent combination prior to deposition. Sugiura et al. used this principle in a two-step procedure to deposit matrix over a tissue section.9 The method named “spray droplet”, involved spray-coating the matrix in humid conditions and in low concentration (the seeding step) followed by microspotting matrix at a higher concentration using a chemical inkjet printer. The control over iterative spray-coating cycles and humidity made this procedure very efficient in terms of ion population (m/z range of 4
20 kDa) and ion intensity compared to the single-step conventional deposition method. Although not fully embraced by the MALDI MSI community, a number of other deposition methods have been shown to improve the ion intensity and to yield more populated mass spectra. These methods are based on the use of “dry” matrix, which in most cases acts as a seeding agent. Aerni et al. were the first to report the use of ground matrix powder being brushed off a sample surface and subsequent matrix microspotting using an acoustic ejector.3 Powder seeding prior to matrix microspotting yielded more homogeneous matrix spots and smaller crystals, and although it did not produce any ion signal without subsequent spotting, it greatly improved the total ion count (TIC) (m/z 5
8 kDa). In 2007 Hankin et al. demonstrated that matrix powder could indeed be used to generate ions and ion images by sublimation and compared this method with conventional electrospray deposition.10 In the new method, the dry matrix was sublimed under vacuum and required the optimization of a range of parameters including pressure, condenser temperature, amount of matrix, heat applied to the matrix, and sublimation time. Although the method required laborious fine-tuning of all these parameters, it yielded a homogeneous coating and higher intensity phospholipid signals and corresponding distribution maps in sections of mouse brain. In 2008 Puolitaival et al. published the use of a solvent-free matrix dry-coating method that allowed detection and mapping of phospholipids with a 30
100 μm lateral resolution.11 In their work, the matrix was finely ground simply using a mortar and pestle and applied by using a 20 μm sieve. Although they did not directly compare the method with that of Hankin et al., a comparison was made with a spray-coating method using a TLC nebulizer. Whereas the quality of the molecular images and the phospholipid localization were very similar to those achieved with the spray-coating, the authors claimed simplicity of sample preparation and minimization of the analyte delocalization as advantages of their method over the classical one. This method has been successfully used later to map and quantify small molecules by Goodwin and co-workers.12,13 Here is reported an alternative two-step matrix deposition procedure that we named the “dry
wet” method which, though potentially applicable to a variety of sections/samples, was specifically developed for the analysis of latent fingermarks. By embracing the advantages of previous methods (seeding through powdering and use of solvent for efficient analyte extraction and cocrystallization), it is possible to demonstrate the superiority of this procedure over the pneumatically assisted matrix spraycoating in particular for fingermark analysis by MALDI MSI. In our method, prior to MALDI MSI analysis, the fingermark is dusted with ground matrix and then sprayed using a solvent in which both the matrix and the analytes dissolve well. In the present work, the dry
wet method proved to be reproducible and superior, compared to conventional spray-coating deposition, in terms of time and extended classes of detectable analytes; given the number of layers needed for the spray-coat and the dry
wet

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method (four and three, respectively) and the time required for the matrix preparation in both cases, the fingermark preparation requires 60 min using the spray-coat method and 40 min using the dry
wet method. The higher the number of fingermarks to process, the greater impact this time difference has. These authors have previously reported on MALDI MSI as a novel analytical tool for the multi-informative analysis of latent fingermarks using classical spray-coating.14 However, given the invisible nature of latent fingermarks, a major limitation in the applicability of the technology existed in the impossibility to proceed with the actual MALDI MSI analysis if the fingermark was not previously enhanced. The enhancement process needs to be compatible with the MALDI MSI analysis, and the fingermark needs to be recovered and laid on a flat and thin surface (less than 200 μm) for instrumental analysis. The dry
wet method bridges the gap between visualizing, recovering, and analyzing a latent fingermark by MALDI MSI as the matrix acts as a dusting (and therefore enhancing) agent. Currently employed enhancement methods can be categorized as optical, physical, physicochemical, or chemical, commonly used examples of each being UV light, black powder, cyanoacrylate fuming, and ninhydrin, respectively. The Home Office Scientific Development Branch (HOSDB, previously Police Scientific Development Branch) edit and publish the Manual of Fingerprint Development Techniques based on their research and testing.15 The manual details the techniques that have been approved for operational use and the order in which they should be applied for a specific set of conditions (primarily surface type and contact with water). The processing flowcharts are organized at the first level by the type of surface on which the fingermark is deposited: smooth nonporous, rough nonporous, paper and cardboard, plastics, metal, raw wood, leather, adhesivecoated surfaces, etc. This necessarily means that the choice of enhancement technique depends largely on the type of deposition surface rather than the chemical composition of the fingermark in question. In the present work we demonstrate that the dry
wet method allows images of latent fingermarks to be obtained after recovery from different surfaces including glass, metal, plastic, wood, and leather. Ungroomed fingermarks (fingermarks with the lowest amount of endogenous compounds) were employed to demonstrate the feasibility of the method and sensitivity of the technology. The positive data obtained give MALDI MSI a further degree of versatility and demonstrate its potential for being integrated within standard operational procedures for the forensic analysis of latent fingermarks.

’ EXPERIMENTAL SECTION MALDI MSI Instrumentation. All mass spectrometric analyses were conducted using a modified Applied Biosystems API Q-Star Pulsar i hybrid quadrupole time-of-flight (QTOF) instrument. The orthogonal MALDI source has been modified to incorporate a SPOT 20 kHz Nd:YVO4 solid-state laser (Elforlight Ltd., Daventry, U.K.), having a wavelength of 355 nm, a pulse duration of 1.5 ns, and producing an elliptical spot size of 100  150 μm2. Images were acquired using “oMALDI Server 5.1” software supplied by MDS Sciex (Concord, Ontario, Canada). MALDI-TOF-MS and MSI Analyses. MALDI-TOF-MSI analyses were performed at a resolution of 100 μm  150 μm using “continuous raster imaging” at a laser repetition rate of 5 kHz. This differs from the classic “stop-and-go fashion” of MALDI 5586

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Analytical Chemistry MSI, as the laser moves continuously in rows across the sample surface allowing rapid acquisition at a high image resolution. Images of a whole fingermark were obtained in around 1 h and 20 min. Data processing was performed using BioMap 3.7.5 software (Novartis, Basel, Switzerland). MALDI MS images showing detection and distribution of different compounds, for the reconstruction of a useful fingermark image, were not normalized. Normalization against the matrix signal at m/z 190 was applied when comparing distribution of the same ion species using the spray-coat and the dry
wet method. Fingermark Preparation. Ungroomed fingermarks were prepared by preliminarily cleaning hands with alcohol wipes (Sheffield branches of Wilkinson’s, Worksop, U.K.) and carrying on normal work activities for a period of 15 min before deposition. The marks were laid onto the ALUGRAM SIL G/UV254 precoated aluminum sheets (Sigma-Aldrich, Poole, U.K.) after scraping off the silica with acetone. Ungroomed fingermarks were also deposited on a knife (metal, nonporous surface), an airtight plastic container (nonporous surface), a laboratory beaker (glass, nonporous surface), a wooden tray (thin cracked varnished wood, semiporous), and a belt (leather, surface treatment not specified, semiporous surface). Fingermarks were also deposited on the same airtight plastic container and laboratory beaker and aged for 10 days under controlled conditions of temperature (25 °C), humidity (60% Hr) and constantly in darkness using an environmental chamber (Sanyo, Loughborough, U.K.) Application of the Matrix. For the dry
wet method a pestle and mortar was employed to grind R-cyano-4-hydroxycinnamic acid (R-CHCA) into a very fine powder, which was used to dust the fingermark using a Zephyr brush. Excess powder was then removed using a Klenair air sprayer (Kenco Ltd., Swindon, U.K.). We have estimated that, for a fingermark area of the size of 2 cm  1.3 cm, ∼0.5 mg of matrix is eventually present on the fingermark. This estimated figure has been reached by weighing the support with the deposited fingermark prior to matrix dusting and after blowing matrix excess off following dusting. The aluminum sheet with the dusted fingermark on it was then stuck onto a MALDI spotless “OPTI-Tof” insert using double-sided conductive carbon tape and sprayed with three layers of a 70:30 ACN/0.5% TFA solution using the SunCollect autosprayer (SunchromGmbH, Friedrichsdorf, Germany), at a flow rate of 2 μL/min. Fingermarks deposited on the different surfaces employed were dusted and lifted with CSI tape (TETRA Scene of Crime, http://www.tetrasoc.com/). The tape was then stuck using double-sided conductive carbon tape (TAAB, Aldermaston, U.K.) onto a MALDI OPTI spotless insert (Applied Biosystems, CA, U.S.A.). The tape containing the fingermark was then sprayed in the same fashion with three layers of 70:30 ACN/0.1% solution. Fingermarks deposited on TLC aluminum supports were also sprayed using the classic spray-coat method as described by Wolstenholme et al.14 Photography of the Fingermark Evidence. Digital images were obtained using a Fujifilm IS Pro, 3488  2616 pixel CCD camera, with a Fujinon 50 mm UV lens. The size of the image obtained was 4256  2848 pixels. Fluorescence Visualization of Fingermarks. UV
vis and fluorescent images of fingermarks, prepared with the dry
wet method, were obtained using (i) a video spectral comparator (VSC4CX, Foster & Freeman, Evesham, U.K.) at an excitation wavelength of 365 nm, (ii) an Olympus BX51 fluorescent microscope equipped with Cell-D software (Olympus), using a

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Figure 1. Potential forensic fingermark examination workflow. The dry
wet method allows multiple analytical protocols to be applied for a more informative fingermark examination. The latent fingermark present at a simulated crime scene (A) can be enhanced by dusting with a MALDI matrix (here, R-CHCA was employed) and photographed (B). The dusted fingermark can absorb UV light (here a UV lamp at 365 nm was used); therefore, the evidence exhibits much clearer ridge details for a more accurate database comparison (C). The matrix employed is also fluorescent; therefore, the dusted fingermark can subsequently be inspected by using a fluorescent microscope. The magnification employed (40) allows accurate visualization of the minutiae; panel D reports the image of the fingermark loop highlighted by the insert in panel C. The fingermark can finally undergo MALDI MSI analysis for obtaining chemical information, which can potentially add intelligence to the case; panel E shows the mass image of the species at m/z 304 previously identified as dimethylbenzylammonium ion.

U-MNU2 filter (excitation 360
370 nm, 400 nm dichromatic, emission 420 nm) and (4) objective.

’ RESULTS AND DISCUSSION A novel two-step matrix deposition method (the dry
wet method) has been devised and applied to the analysis of latent fingermarks. The first step involves the application of finely ground MALDI matrix to the fingermark, in this case R-CHCA. Molecular sieves, as indicated by Puolitaval et al.,11 were initially tested, but their use was later dismissed as filtering the matrix in such a way proved to be very laborious and time-consuming, with no significant improvement in the results obtained as well as being impractical for vertical surfaces. Additionally, dusting fingermarks is one of the conventional methodologies used by forensic investigators to develop marks at the crime scene; therefore, if introduced, this would be a familiar procedure for CSI officers. The second step involves the spraying of the matrix dissolution solvent. In the first step of the method, the matrix acts as an enhancer, and after blowing away excess, a photograph can be taken, as Figure 1 shows, and sent to the laboratory for scanning and comparison using police databases. Figure 1A shows a photograph of the fingermark prior to matrix dusting. After matrix application, a very clear ridge pattern is visualized (Figure 1B) where the minutiae (local features of the ridge pattern) can be very clearly observed. According to the HOSDB grading system, where the proportion of the developed fingerprint with clear ridge detail is estimated and a score is assigned to the fingerprint from 0 to 4, the fingerprint could be classified as grade 4 (full development
whole fingerprint in clear continuous ridges). Another interesting aspect to this protocol is due to the R-CHCA matrix’s property to fluoresce; fluorescent optical images could also be taken either as a whole, using a simple device like a document examination instrument operated at a wavelength of 365 nm, or as small areas when using a fluorescent microscope operated as described in the Experimental Section (Figure 1, parts C and D). The magnification employed on the fluorescent 5587

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Figure 2. Detection of a wide range of fingermark endogenous compounds by using the dry
wet method and subsequent MALDI MSI analysis. Panel A displays the comparative analysis of species that have been putatively assigned as amino acids imaged with the dry
wet and the spray-coat methods (images are normalized against the R-CHCA matrix ion signal at m/z 190) showing for these species a far greater sensitivity when using the dry
wet method. A selection of fingermark mass images is shown in panel B (images are not normalized here but optimized for contrast and brightness). The method allows the distribution of a variety of putative endogenous species including amino acids (first row), fatty acids and vitamins (second row), diacylglycerols (DG, third row), and triacylglycerols (TG, fourth row) to be mapped from an ungroomed fingermark.

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microscope (40) allowed the fingermark to be inspected with a high level of detail. The same fingermark can be subsequently subjected to MALDI MSI (Figure 1E) allowing an image of the ridge pattern and, potentially, chemical information from the endogenous and exogenous compounds present in the fingermark to be obtained simultaneously. The possibility to acquire two different optical images prior to MALDI MSI analysis is very important as it enables evidence to be provided quickly and in a court of law in a currently accepted forensic fashion. The concept of a multipurpose dusting agent has been reported by Rowell et al.;16 they employed a hydrophobic silica dusting agent containing carbon black which enabled both visualization and surface-assisted laser desorption ionization time-of-flight mass spectrometry (SALDI-TOF-MS) analysis of the latent fingermarks. The chemical was a particularly good SALDI matrix targeting a range of drugs. Although chemical information could be obtained, SALDI-TOF-MS was not shown to provide a chemical image of the actual fingerprint to complement the optical one. The dry
wet method allows instead chemical information to be recovered embedded in multiple MS images. The dry
wet method devised allows images of fingermarks to be obtained showing detection of many molecular species, comparable to those previously reported by spray-coating the matrix.14 Interestingly, some of the species imaged with the dry
wet method were absent using the spray-coat method. As an example, Figure 2A reports the comparative analysis of species that have been putatively assigned as amino acids imaged with the dry
wet and the spray-coat methods (Figure 2A, images are normalized against matrix ion signal at m/z 190); with the spraycoat method, only in the case of putative histidine is it possible to observe a very faint image of the upper part of the fingermark, which nonetheless is of a very bad quality (grade 0). In all other cases, there was no retrievable image of amino acids when the spray-coat method was employed. Using the dry
wet method, a sample of species detected, imaged, and putatively assigned, including phospholipids, amino acids, vitamins, fatty acids, di- and triacylglycerols, is shown in Figure 2B from yet another donor. This is a particularly important advantage of the method as it shows the versatility of MALDI MSI compared to other currently used forensic technologies that need to be selected according to the molecular target. When the particular distribution of a certain species is of interest (for example, illicit substances) on an absolute scale or in relation to other substances, or when a comparison of the distribution of the same substance within two fingermarks is made, images would need to be normalized and the same contrast/brightness should be applied. When the aim is obtaining an image that shows clear ridge pattern details for a fingermark area that is as large as possible, presence of particular compounds (rather than relative amounts) can be visualized in images by skipping the normalization process if this reduces the number of minutiae retrievable. Therefore, all the images presented in this paper (with the exception of Figure 2A showing a comparison of distribution of the same ion species using the spray-coat and the dry
wet methods) have not been normalized and the contrast/brightness has been optimized for each individual image. Reproducibility of the dry
wet method was also tested by imaging four fingermarks from the same donor prepared as reported in the Experimental Section. Average spectra were exported from Biomap to mMass, which is an open source multifunctional mass spectrometry software.17,18 Figure 3a reports the four mass 5588

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Figure 3. MALDI MSI reproducibility study. Panel a shows the superimposition of the R-CHCA ion signal at m/z 190 from the four fingermark replicates prepared using the dry
wet method. The ordinate scale is the arbitrary intensity scale directly provided by the spectrometer without further processing. An exogenous signal at m/z 304 (dimethylbenzylammonium ion, DBA), also producing superimposable spectra (panel b), was mapped showing four reproducible images of a delta minutia present in the fingermark examined.

spectra generated for the R-CHCA matrix peak at m/z 190. Spectra were not normalized. The ion peak signals exhibited good reproducibility in terms of ion intensity, thus showing reproducibility in the application of the matrix. The lack of a perfect superimposition is likely due to the impossibility of obtaining four identical fingermark depositions as the pressure that the finger exerts on the surface will be inevitably slightly different. Before the deposition of ungroomed fingermarks (as described in the Experimental Section), hands and fingers were wiped with alcohol wipes known to contain an antiseptic, dimethylbenzylammonium ion, which has previously been identified by these and other authors19,20 and observed to generate very good mass spectral images.18 Dimethylbenzylammonium ion mass spectra are therefore also reported in Figure 3b showing again a good reproducibility of the ion signal intensity to a similar degree to that observed for the matrix. Mass images of this ion are also shown (Figure 3b) reflecting the average peak intensities observed in the mass spectra of the four replicates and the possibility to detect with constant clarity the “delta” feature which is one of the minutiae exhibited by the particular fingermark examined. Most importantly, the dry
wet method has a crucial feature which makes it altogether superior to the spray-coating method previously employed by these authors;14 the spray-coating method in fact can only be applied to (a) fingermarks previously enhanced (provided that the enhancing method was compatible with the MALDI MSI analysis) and (b) to fingermarks that were laid flat on an adequate MALDI support. Wolstenholme et al. used only one surface (aluminum sheets) for depositing and analyzing the fingermark, and therefore, the technology could not be proven, at that time, to be helpful in real crime scene investigations. With the dry
wet method instead, using as enhancing powder an actual MALDI matrix, it is now possible to actually visualize fingermarks on crime scene surfaces, lift and then analyze them by MALDI MSI. A range of deposition surfaces have been tested to prove feasibility including nonporous surfaces such as metal, glass, plastic, and semiporous surfaces such as varnished wood and

leather. Figure 4 shows the deposition surfaces employed prior to (Figure 4a
e) and post dusting (Figure 4a1
e1) and the same sample of fingermark mass images for each of them. In particular, images of an endogenous amino acid (putative valine m/z 118), an endogenous fatty acid (oleic acid m/z 283 previously confirmed by MS/MS14,20), and an exogenous compound (dimethylbenzylammonium ion m/z 304, previously confirmed by MS/MS14) are reported. It is known that porous surfaces are more problematic to visualize than nonporous ones; however, a comparison of the ion yield in terms of image and ion intensity according to the different deposition surfaces using the dry
wet method is out of the scope of the present work. As proving feasibility of the method is the aim, all the images are reported with differing contrast and brightness to enhance the ridge detail features in each case. This is how forensic investigators would treat the fingermark image for comparison as their goal is to obtain as many clear minutiae as possible. Figure 4 shows that for all of the tested surfaces it was possible to retrieve an image of the two endogenous and the selected exogenous compounds. In particular, the dimethylbenzylammonium ion exhibits the best image quality (grade 4), which, among other factors, could also be due to its relative amount compared to the two endogenous compounds selected. Although ranging in grade, putative valine and oleic acid overall yield useful images, which could be superimposed using appropriate software to enhance the ridge pattern clarity. Preliminary data further show applicability of the overall methodology even for aged fingermarks. As an example, Figure S-1 (Supporting Information) shows mass spectral profiles of oleic acid and dimethylbenzylammonium in fresh and aged fingermarks (10 days at 25 °C and 60% Hr in dark conditions). Fingermarks were deposited on two of the same surfaces shown in Figure 4, that is glass (one of the best surfaces in terms of fingermark recoverability in this study) and on plastic (one of the worst); the species could be detected and imaged even 10 days after deposition. This experiment proves that, although the quality of the images from 10 day aged fingermarks is not always as good as that from fingermarks immediately recovered, chemical information can still be obtained. Additionally, in most of the 5589

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components in one analysis and simultaneously providing an image of the fingermark ridge pattern. In this paper it is demonstrated that, additionally, MALDI MSI can be used for fingermarks deposited on a range of surfaces and in such a way that recovery from the scene could be integrated easily with current crime scene investigator practice for subsequent instrumental analysis. The novel two-step matrix deposition method that has been developed allows evidence to be photographed and exposed to both UV light and fluorescent radiation thus enabling even clearer images to be obtained. This possibility allows the kind of evidence produced currently in a court of law to be generated prior to subsequent MALDI MSI analysis which, by providing chemical information, potentially adds intelligence to the case under investigation. Work is in progress to improve the application of the matrix in the first step of the dry
wet method as well as to extend its applicability to a wider range of surfaces.

’ ASSOCIATED CONTENT

bS

Figure 4. Recovery and MALDI MSI analysis of ungroomed fingermarks lifted from different surfaces including glass, metal, wood, plastic, and leather (panels a
e). Corresponding MALDI MS images have not been normalized and have been flipped left to right to facilitate a visual comparison with the dusted optical images. The dry
wet method has been tested by dusting the fingermarks with R-CHCA (panels a1
e1), which were then lifted, sprayed with the appropriate solvent, and submitted to MALDI MSI analysis. Representative MS images of an endogenous amino acid (putative valine m/z 118), an endogenous fatty acid (oleic acid m/z 283), and an exogenous compound (dimethylbenzylammonium ion, DBA, m/z 304) are shown for each deposition surface.

realistic scenarios, fingermarks would be recovered within 48 h, a lot earlier than the aging time we have used in this experiment. The demonstrated applicability of the dry
wet method to recover and analyze latent fingermarks by MALDI MSI complements the achievements of current forensic methodologies; as the techniques suggested in the HOSDB manual are aimed solely at providing an image of the ridges on the fingertip, they are often not appropriate for a wide range of scenarios and they do not provide any additional information. Only in cases where a clear mark has been deposited will the current techniques, if used correctly, allow a comparison. However, scene of crime marks are not ideal marks. They may be smudged, as a result of the articulation of the arm while the donor is holding an object, overlaid because of multiple contacts, or any number of other scenarios resulting in ridges that are not sufficiently clear for comparison. In these cases it would be beneficial to have a protocol available, such as MALDI MSI in combination with the dry
wet deposition method, that is able to make the ridge pattern visible, where that is possible, but also one that can provide chemical information (for example, donor dietary habits or drug use) where it is not.

’ CONCLUSIONS These authors have previously shown that MALDI MSI is capable of detecting both endogenous and exogenous fingermark

Supporting Information. MALDI MSI analysis of aged fingermarks recovered from glass and plastic, showing, in black, the mass spectral profiles of fingermarks deposited on glass and plastic surfaces and recovered immediately after by using the dry
wet method and, in red, the mass spectral profiles of fingermarks aged for 10 days at 25 °C and 60% Hr (in dark conditions) prior to recovery and analysis; the species at m/z 283.2 (oleic acid) and 304.2 (dimethylbenzylammonium ion), although exhibiting a lower signal intensity, are still detected and imaged 10 days after deposition (Figure S-1). This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*Phone: þ441142256165. Fax: þ441142253066. E-mail: s.francese@ shu.ac.uk.

’ ACKNOWLEDGMENT The work presented is based on the prior patent claim filed on March 9, 2011, U.K. Patent Number 1104003.7. The British Mass Spectrometry Society is gratefully acknowledged for awarding a summer studentship to Robert Bradshaw who worked on the enhancement and MALDI MSI analysis of fingermarks recovered from different surfaces. ’ REFERENCES (1) Sloane, A. J.; Duff, J. L.; Wilson, N. L.; Gandhi, P. S.; Hill, C. J.; Hopwood, F. G.; Smith, P. E.; Thomas, M. L.; Cole, R. A.; Packer, N. H.; Breen, E. J.; Cooley, P. W.; Wallace, D. B.; Williams, K. L.; Gooley, A. A. Mol. Cell. Proteomics 2002, 1, 490–499. (2) ChiP application note. http://www.maldi-msi.org/download/ Biotech%20Shimadzu%20Note.pdf (accessed Nov 5, 2010). (3) Aerni, H. R.; Cornett, D. S.; Caprioli, R. M. Anal. Chem. 2006, 78, 827–834. (4) Portrait 630, application note [online]. http://www.labcyte. com/_fileupload/Image/Por.prod.sheet.pdf (accessed Nov 15, 2010). (5) Caprioli, R. M.; Farmer, T. B.; Gile, J. Anal. Chem. 1997, 69, 4751. (6) Kaletas, B. K.; van der Weil, I. M.; Staube, J.; Dekker, L. J.; Guzel, C.; Kros, J. M.; Luider, T. M.; Heeren, R. M. A. Proteomics 2009, 9, 2622–2633. (7) Stoeckli, M.; Staab, D.; Staufenbiel, M.; Wiederhold, K. H.; Signor, L. Anal. Biochem. 2002, 311, 33–39. 5590

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’ NOTE ADDED AFTER ASAP PUBLICATION This paper was published on the Web on June 13, 2011. An addition was made to the Acknowledgment regarding a patent filing, and the corrected version was reposted on June 23, 2011.

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dx.doi.org/10.1021/ac200619f |Anal. Chem. 2011, 83, 5585–5591