Examining latent fingerprints using atomic force microscopy

Abstract

A method for creating an image of a latent print. The method includes applying a polymer to a surface, wherein the latent print is located on the surface. The method includes forming a negative impression of the latent print on the polymer. The method includes lifting the polymer from the surface after a period of time to obtain a lifted polymer comprising the negative impression of the latent print. The method includes scanning the negative impression of the latent print on the lifted polymer using a microscope to create the image.

Description

EXAMINING LATENT FINGERPRINTS USING ATOMIC FORCE MICROSCOPYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of priority to U.S. Provisional Application Serial No. 63 / 552,964, filed on February 13, 2024, which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure relates to examining latent fingerprints or toeprints using lithography and microscopy.BACKGROUND

[0003] Crime scene examination is essential to the modern criminal justice system. As part of the examination, crime scene investigators document a potential crime scene for evidence. This includes taking photographs of the scene, collecting forensic evidence, and maintaining a proper chain of custody of the evidence. Common types of forensic evidence include ballistics, blood tests, deoxyribonucleic acid (“DNA”) tests, and latent prints (e.g., fingerprints). A latent print is an impression of sweat, dirt, microorganisms, oils, or other residue present on skin that has been transferred to another surface. The permanent and unique arrangement of the features of this skin allows for the identification of an individual to a latent print.

[0004] The imaging (i.e., detection) of latent fingerprints remains among the most challenging. This is particularly so for the reason that a latent fingerprint can only become visible by application of an imaging enhancement technique. Latent print visualization with powder is a conventional method for examining latent prints. This method involves applying a fine powder to the latent prints which physically adheres to the aqueous and oily components in the print. The powder may then be transferred to another surface where it can be compared to other fingerprints in a database. The comparison may include examining tiny ridges, whorls, and valley patterns of the print. Typical methods for latent print evaluation, however, are time consuming and require transferring the copy of the print to multiple locations. Additionally, the prints discovered at a crime scene are often incomplete (partial) and can yield disappointing results when compared for analysis. Accordingly, there is a need for a portable and efficient process to evaluate latent prints.SUMMARY

[0005] In one aspect, the present disclosure includes a method for creating an image of a latent print. The method includes applying a polymer to a surface. The latent print is located on the surface. The method includes forming a negative impression of the latent print on the polymer. The method includes lifting the polymer from the surface after a period of time to obtain a lifted polymer comprising the negative impression of the latent print. The method includes scanning the negative impression of the latent print on the lifted polymer using a microscope to create the image.

[0006] In one aspect, the present disclosure includes a kit comprising microscope slides, one or more cleaning reagents, one or more petri dishes, and a polymer having a size suitable to form a negative impression of a fingerprint or a toeprint.

[0007] An advantage of the embodiments disclosed herein is an improvement in latent print examination through the use of atomic force microscopes (“AFMs”). A polymer, such as polydimethylsiloxane (“PDMS”), may be applied to develop a negative of a latent print. A mobile AFM may be deployed to scan the negative which allows for a rapid and accurate examination of the latent print.BRIEF DESCRIPTION OF DRAWINGS

[0008] An understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention may be utilized, and the accompanying drawings of which:

[0009] Fig. 1 shows a flow diagram illustrating a process for examining a latent print according to an embodiment.

[0010] Fig. 2 shows a flow diagram illustrating a process for examining a latent print according to an embodiment.

[0011] Fig. 3 shows an AFM raw image of a PDMS negative.

[0012] Fig. 4 shows a graph illustrating contour for a fingerprint ridge in a PDMS negative.

[0013] Fig. 5 shows an AFM scan of a fingerprint on a glass substrate.

[0014] Fig. 6 shows optical microscopy of a fingerprint on glass.

[0015] Fig. 7 shows a raw AFM image of debris caught in a fingerprint.

[0016] Fig. 8 shows an AFM plot of ridge heights.

[0017] Fig. 9 shows an energy dispersive spectroscopy analysis of a fingerprint.

[0018] Fig. 10 shows a histogram plot of elemental prevalence in a fingerprint.

[0019] Fig. 11 shows an energy dispersive spectroscopy analysis of a fingerprint.

[0020] Fig. 12 shows a histogram plot of elemental prevalence in a fingerprint.

[0021] Fig. 13 shows a flow chart of a method according to one aspect of the present disclosure.

[0022] The accompanying drawings illustrate various examples. The skilled person will appreciate that the illustrated element boundaries (e.g., boxes, groups of boxes, or other shapes) in the drawings represent one example of the boundaries. It may be that in some examples, one element may be designed as multiple elements or that multiple elements may be designed as one element. Common reference numerals are used throughout the figures, where appropriate, to indicate similar features. The figures herein are for illustrative purposes only and are not necessarily drawn to scale.DETAILED DESCRIPTION

[0023] The following description is made for the purpose of illustrating the general principles of the present technology and is not meant to limit the inventive concepts claimed herein. As will be apparent to anyone of ordinary skill in the art, one or more or all of the particular features described herein in the context of one embodiment are also present in some other embodiment(s) and / or can be used in combination with other described features in various possible combinations and permutations in some other embodiment(s).

[0024] The present disclosure is directed to a method for creating an image of a latent print on a surface. The image will elucidate the macrostructural features (e.g., overall shape and / or patterns) of the print. A pattern can include any of the surface structural details of the object that made the print on the surface. The surface structural details include, for example, the full or partial outline of the print, and / or surface features, such as raised portions (e.g., ridges), recessed portions, protruding portions, unique markers, or identifiers, and the like.

[0025] In some aspects, the present disclosure is directed to a kit or portable system for use according to the methods of the present disclosure. In some aspects, the kit or portable system may include one or more microscope slides, one or more cleaning reagents, one or more petri dishes, and a polymer having a size suitable to form a negative impression of a fingerprint or a toeprint. In some aspects, practitioners such as investigators or members of law enforcement agencies may use the kit or portable system for latent fingerprint detection or training purposes.

[0026] Using the method described above, a variety of prints, particularly fingerprints or toe prints, can be conveniently imaged. The method is particularly convenient in that prints can be imaged directly on-site on native surfaces by use of the portable microscopic system described herein.

[0027] Fig. 1 of the accompanying drawings shows a flow diagram illustrating a process 100 for examining a latent print 102 according to an embodiment. Process 100 may begin with step slOl. At slOl, process 100 includes applying a polymer 104 to a surface. Latent print 102 may be located on the surface. At si 03, process 100 includes lifting polymer 104 from the surface after a period of time. The lifted polymer is a negative 106 of latent print 102. At sl05, process 100 includes scanning negative 106 of latent print 102 using an AFM.

[0028] The present disclosure creates a negative of the latent print rather than creating a reproduction, replica, or “phantom” of the print. Further, according to the present disclosure, the negative is scanned directly using microscopy, e.g., AFM, rather than the negative being used to mold a reproduction, replica, or “phantom” of the print from the negative. Further, the present disclosure is directed to latent prints on a surface rather than for use on a finger or on a mold of a finger.

[0029] In some embodiments, the period of time is a curing time for polymer 104 and polymer 104 includes poly dimethylsiloxane (PDMS). PDMS is a family of polymers tailored with different cure times, cure temperatures, and mechanical properties. For example, polymer 104 may include DOW SylgardTM 184 or DOW SylgardTM 182, which has a longer working time (longer room temperature cure) than DOW SylgardTM 184.. In some aspects, polymers useful for micromanufacturing, including in lab-on-a-chip microfluidic devices, may be included in polymer 104. According to the present disclosure, PDMS is a curable elastomer that can function as a flexible negative. PDMS negatives are more resilient to deformation and smudging than raw oils in fingerprints.

[0030] Polymer 104 may be cured at room temperature or by utilizing a heating element. The curing time for polymer 104 may be dependent on the quantity of polymer 104 applied and the temperature of polymer 104 (e.g., heating polymer 104 may reduce the curing time).

[0031] Polymer 104 may include enhancement materials, such as, dyes, powders, and / or fluorescents. The enhancement materials may be mixed into polymer 104 and may improve optical and atomic force microscopy by modifying the optical and mechanical properties of negative 106. In some embodiments, polymer 104 may include epoxy resins, urethane rubbers, or fluoropolymers such as polytetrafluoroethylene (PTFE / Teflon).

[0032] In some embodiments, process 100 includes preparing the surface for polymer application and performing energy dispersive spectroscopy on the surface. Salt deposited from print contact with the surface may be detected by energy dispersive spectroscopy. The main debris and carbon found in energy dispersive spectroscopy may be derive from sebum-related hydrocarbons excreted by the skin. Energy dispersive spectroscopy may be performed by ascanning electron microscopes (“SEM”). In some embodiments, the SEM may be operated at 15kV with a working distance (WD) of 8.4-8.6mm.

[0033] The AFM may be operated in contact mode, with a 1 lOum field of view, and a scan rate of 1 second. Scanning negative 106 of latent print 102 reveals ridges which correlate to low regions of the latent print. In some embodiments, latent print 102 is a fingerprint and negative 106 may be used as a stamp to recreate the fingerprint. For example, negative 106 may be placed in ink, dye, or other fluorescents and then applied to a surface for fingerprint imaging. The recreated fingerprint may be compared to other fingerprints in a database.

[0034] Process 100 may be used in the identification of latent prints on a surface or in cold case files to more accurately identify individuals and identify foreign matter that could be used as evidence. The identification of latent prints according to the present disclosure may include ridge comparisons which could be used to determine the age of an individual through analysis. Process 100 may be performed at a relatively low cost. For example, the present disclosure includes mobile nano-analysis laboratories with AFMs that can be deployed rapidly to crime scenes. AFMs have manageable initial costs and footprints, which allow widespread adoption of advanced characterization tools capable of greater feature extraction utilizing sub-micron resolutions.

[0035] Fig. 2 of the accompanying drawings shows a flow diagram illustrating a process 200 for examining a latent print according to embodiment. Process 200 may begin with step s201. At s201, latent oils / ridges 202 of a latent print are applied to a substrate 204. Latent oils / ridges 202 may be applied when a person touches surface 204 with their finger. When the finger is removed, it leaves behind latent oils / ridges 202 on surface 204. Latent oils / ridges 202 have a pattern associated with the person.

[0036] At s203, PDMS 206 is applied to surface 204. PDMS 206 is initially a liquid and flows around latent oils / ridges 202. At s205, PDMS 206 cures and solidifies to form PDMS negative 208. When PDMS negative 208 is removed from substrate 204, it include a negative of the pattern of oils / ridges 202. PDMS negative 208 may be scanned by an AFM to examine the latent print.

[0037] Fig. 3 of the accompanying drawings illustrates an AFM raw image 300 of a PDMS negative. AFM raw image 300 is a heatmap of heights across the surface of the PDMS negative. The lighting of AFM raw image 300 indicates a relative height of the PDMS negative with the darker portions indicating a lower relative height and the lighter portions indicating a higher relative height. Fig. 4 of the accompanying drawings shows a graph 400 illustrating contour for a fingerprint ridge in a PDMS negative. The y-axis is a relative height in nanometers andthe x-axis is the distance across the PDMS negative in micrometers. The relative height is measured with the shallowest point (i.e., lowest relative height) of the PDMS negative marked at zero. Specifically, graph 400 illustrates contour of the PDMS negative of Fig. 3 across section 302.

[0038] The invention is further described in the following example, which does not limit the scope of the invention described in the claims and provide proof-of-concept demonstration for the advantageous of the air filtration devices described in the present disclosure.

[0039] In an example, a substrate (e.g., a glass microscope slide) was cleaned via lint-free wipes with 100% isopropyl alcohol (“IPA”) followed by 5 min IPA Sonication and a nitrogen (N2) gas dry. A user's fingerprint for examination was prepared via cleaning the fingerprint with 100% IPA and wipe, followed by wearing a nitrile glove for 5 minutes to allow sufficient sweat to develop. Following this time, the glove was removed and the fingerprint taken.

[0040] Fig. 5 of the accompanying drawings illustrates an AFM scan 500 of a fingerprint on a glass substrate. AFM scan 500 is a 3D view of fingerprint ridges on the glass substrate. The height of the fingerprint ridges are shown on the right side of AFM scan 500 with the peaks of the ridges extending upwards. The left side of AMF scan 500 illustrates the relatively smooth portion of the glass substrate without the fingerprint. The glass substrate may be prepared with a cleaning process. Fig. 6 of the accompanying drawings illustrates an optical microscopy 600 of a PDMS fingerprint negative. Fig. 7 of the accompanying drawings illustrate a raw AFM image 700 of debris caught in the fingerprint. AFM image 700 is a height map taken from debris / oils left inside a fingerprint. The lighter portions of AFM image 700 indicate a greater relative height and the darker portions indicate a lower relative height.

[0041] Fig. 8 of the accompanying drawings shows a graph 800 illustrating contour for debris caught in the fingerprint. The y-axis is a relative height in nanometers and the x-axis is the distance across the fingerprint in micrometers. The relative height is measured with the shallowest point (i.e., lowest relative height) of the fingerprint marked at zero. Specifically, Fig. 8 of the accompanying drawings illustrate a graph of the height of debris across section 702 of Fig. 7.

[0042] Fig. 9 of the accompanying drawings illustrates a zoomed-out view 900 of concentric fingerprint ridge oils / debris of an energy dispersive spectroscopy analysis of a fingerprint.

[0043] Fig. 10 of the accompanying drawings illustrates a histogram plot 1000 of elemental prevalence of the energy dispersive spectroscopy analysis.

[0044] Energy dispersive spectroscopy (“EDS”) is an x-ray technique performed in the SEM.

[0045] EDS may include Energy-dispersive X-ray spectroscopy (EDS, EDX, EDXS or XEDS), which is sometimes called energy dispersive X-ray analysis (EDXA or EDAX) or energy dispersive X-ray microanalysis (EDXMA).

[0046] Empty substrates, substrates bearing fingerprints, and PDMS negatives of fingerprints were loaded into a desktop SEM with an Energy Dispersive X-ray Spectroscopy (EDS / EDX / etc.). This tool was used to characterize the elemental composition of debris found in the samples. In EDX, a “map” of elements is produced, so the user can observe the location and quantity. Fig. 11 of the accompanying drawings illustrates a zoomed-in view 1100 of the energy dispersive spectroscopy analysis of Fig. 9 on a mass of sweat and salt. Fig. 12 of the accompanying drawings illustrates elemental prevalence 1200 of a mass of sweat and salt of Fig. 9.

[0047] Fig. 13 of the accompanying drawings illustrates a process 1300, according to an embodiment, for creating an image of a latent print. Process 1300 may begin with step 1302. Step 1302 comprises applying a polymer to a surface. The latent print is located on the surface. Step 1304 comprises forming a negative impression of the latent print on the polymer. Step 1306 comprises lifting the polymer from the surface after a period of time to obtain a lifted polymer comprising the negative impression of the latent print. Step 1308 comprises scanning the negative impression of the latent print on the lifted polymer using a microscope to create the image.

[0048] In some embodiments, the scanning step is performed using an atomic force microscope (AFM). In some embodiments, the scanning step is performed using a scanning electron microscope (SEM). In some embodiments, process 1300 further comprises pretreating the surface for polymer application before the applying step.

[0049] In some embodiments, the period of time is a curing time for the polymer. In some embodiments, the polymer comprises polydimethylsiloxane (PDMS). In some embodiments, the polymer comprises an epoxy resin, urethane rubber, or fluoropolymer. In some embodiments, the polymer comprises polytetrafluoroethylene (PTFE / Teflon).

[0050] In some embodiments, process 1300 further comprises performing energy dispersive spectroscopy on the surface. In some embodiments, process 1300 comprises performing the scanning step and the AFM is in contact mode. In some embodiments, process 1300 comprises performing the scanning step and the AFM has a 90-150 um field of view, a 100-140 um field of view, a 105-135 um field of view, a 110-130 um field of view, a 110-120um field of view, or a 110 um field of view. In some embodiments, process 1300 comprises performing the scanning step and the AFM has a scan rate of 1 second.

[0051] In some embodiments, process 1300 further comprises mapping ridges corresponding to low regions of the latent print during the scanning step. In some embodiments, process 1300 further comprises performing x-ray analysis of debris during or after the scanning step. In some embodiments, process 1300 further comprises performing energy dispersive spectroscopy during or after the scanning step.

[0052] In some embodiments, the energy dispersive spectroscopy comprises scanning electron microscopy to detect one or more salts, carbon-containing matter, compounds excreted by skin, or a combination thereof.

[0053] In some embodiments, process 1300 further comprises measuring ridge height of the negative impression of the latent print to estimate age of a human that left the latent print on the surface. In some embodiments, the latent print is a fingerprint. In some embodiments, the polymer includes a pigment.

[0054] Fingerprint matching software may be used based on the images obtained by the methods of the present disclosure. The method of the present disclosure includes characterizing the location and arrangement of fingerprint ridges in relation to each other, unique ridge patterns formed where ridges come together and differentiate, and width, edge contours, shape, the location and size of sweat pores and other permanent details such as creases or scars.

[0055] While various embodiments are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[0056] As used herein “a” means “at least one” or “one or more.”

[0057] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.

[0058] It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and notlimit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.

[0059] All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition section headings, the materials, methods, and examples are illustrative only and not intended to be limiting.

Claims

CLAIMS:What is claims is:

1. A method (1300) for creating an image of a latent print (102) comprising: applying (1302) a polymer (104) to a surface, wherein the latent print is located on the surface; forming (1304) a negative impression of the latent print on the polymer; lifting (1306) the polymer from the surface after a period of time to obtain a lifted polymer comprising the negative impression (106) of the latent print; and scanning (1308) the negative impression of the latent print on the lifted polymer using a microscope to create the image.

2. The method of claim 1, wherein the scanning step is performed using an atomic force microscope (AFM).

3. The method of claim 1 or claim 2, wherein the scanning step is performed using a scanning electron microscope (SEM).

4. The method of any one of claims 1-3, further comprising pre-treating the surface for polymer application before the applying step.

5. The method of any one of claims 1-4, wherein the period of time is a curing time for the polymer.

6. The method of any one of claims 1-5, wherein the polymer comprises polydimethylsiloxane (PDMS).

7. The method of any one of claims 1-5, wherein the polymer comprises an epoxy resin, urethane rubber, or fluoropolymer.

8. The method of any one of claims 1-5, wherein the polymer comprises polytetrafluoroethylene (PTFE / Teflon).

9. The method of any one of claims 1-8, further comprising performing energy dispersive spectroscopy on the surface.

10. The method of any one of claims 1-9, comprising performing the scanning step wherein the AFM is in contact mode.

11. The method of any one of claims 1-10, comprising performing the scanning step wherein the AFM has a 90-150 um field of view, a 100-140 um field of view, a 105- 135 um field of view, a 110-130 um field of view, a 110-120 um field of view, or a 110 um field of view.

12. The method of any one of claims 1-11, comprising performing the scanning step wherein the AFM has a scan rate of 1 second.

13. The method of any one of claims 1-12, further comprising mapping ridges corresponding to low regions of the latent print during the scanning step.

14. The method of any one of claims 1-13, further comprising performing x-ray analysis of debris during or after the scanning step.

15. The method of any one of claims 1-13, further comprising performing energy dispersive spectroscopy during or after the scanning step.

16. The method of claim 15, wherein the energy dispersive spectroscopy comprises scanning electron microscopy to detect one or more salts, carbon-containing matter, compounds excreted by skin, or a combination thereof.

17. The method of any one of claims 1-16, further comprising measuring ridge height of the negative impression of the latent print to estimate age of a human that left the latent print on the surface.

18. The method of any one of claims 1-17, wherein the latent print is a fingerprint.

19. The method of any one of claims 1-18, wherein the polymer includes a pigment.

0. A kit comprising microscope slides, one or more cleaning reagents, one or more petri dishes, and a polymer having a size suitable to form a negative impression of a fingerprint or a toeprint.

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