Abstract
Here, the use of attenuated total reflectance infrared spectroscopy to analyze latent, lifted fingerprints is examined. Recently, there has been an upsurge in using IR spectroscopy as it can objectively define chemical properties of residues on fingerprints without damaging the sample. The use of fingerprints is heavily weighted in the field of forensics. Determining the chemical composition of the residue on a deposited set of fingerprints can give more insight to the events prior to the deposit of said prints. Here, the use of FTIR-ATR is used to determine whether aspirin can be detected in sample fingerprint. The way the aspirin had contaminated the fingerprint varied in quantity and the way it was collected on the fingerprint.
It is important to understand how fingerprints are lifted in order to account for them in the results. IR spectra generally give insight to all present functional groups including those already known such as the sebaceous fluids which make up the fingerprint and the material found in the lifting tape. As a result, one must be able to somehow account for those functional groups and ensure that the removal of those functional groups will not affect the concluding hypothesis. Here, aspirin was used as it contains ortho substituents on an aromatic ring, both of which are visible on the IR spectrum.
This research lays the foundation for a new method for testing fingerprints which will in turn improve the odds of getting more accurate positives for matching prints. As known, fingerprints are unique but little has been done to improve the system used to analyze fingerprints since the 20th century.
Literature Review
Fingerprints are one of the most valuable types of physical evidence that can be found at the scene of a crime. Since 1860, fingerprints have been used to identify criminals as an identity marker (Chiang, 2012). In fact, Fauld discussed the unique skin ridge patterns which individualized fingerprints (Chiang, 2012). This later led to the development of the first systematic attempt at person identification: Bertillon's system which includes: a print, profile images and a section known as anthropometry: a system of precise body measurements. Today, the Henry system, proposed by Sir Edward Henry is commonly adopted for its simplistic and innovative practice which can accurately determine the identity of a person who test positive for those specific fingerprints.
Early on, three physical shapes of fingerprints have been identified: the loop, whorl and arch (Francis Galton), named after the physical, observable patterns formed by the many ridges. In Galton’s published work, Fingerprints, he stated no two prints are identical. Another observable law stated: an individual's prints will remain unchanged from one year to the next. In this way, one may conclude that the fingerprints one is assigned at birth will remain constant for one’s lifetime. After collecting over 8,000 sets, Galton was able to prove, with data analysis, the individuality of fingerprints to people (Galton). Modern research, such as that performed by Geoffrey et al, 2014 further develop the field’s understanding of the individuality of fingerprints with respect to the genome and has solidified the use of fingerprints to identify a species in a larger portion of the animal kingdom. Overall, it has become well known in the field that fingerprints are unique to each person. This is important to note to ensure that research in this field can be used to identify each individual.
There are three general means to leave a fingerprint on a surface. Prints that have been deposited on any surface, made of the sweat and oil on the skin’s surface fashioned in the same shape of one’s fingerprint is known as a latent fingerprint. Latent prints can be characterized by their lack of pigmentation. These prints may be seen by the naked eye, but are difficult to see overall. Three types of glands, eccrine, apocrine and sebaceous are the three glands which are responsible for the secretions from the fingertips (Bumbrah, 2017).
A print that can be visible is known as a patent fingerprint. There are two means of developing a patent print. Depositing a pigmented print on a contrasting surface is a common way. An example would be lightly coating the ridges of a fingerprint in black ink and depositing it on a white paper (Crime museum). These types of prints can not give much insight into the 3D rendition of the finger. A second type of fingerprint which can be visible is known as a plastic fingerprint which is formed by pressing a fingertip on a surface which can easily change its shape such as wax, tar or drying paint, which creates a three dimensional rendering of the fingerprint (Crime museum). Patent fingerprints and plastic fingerprints are highly visible while latent fingerprints require additional processing for visibility purposes (Crime museum).
Fumigation, also known as cyanoacrylate fuming, or colloquially as the super glue method, is a specific technique used to enhance contaminated fingerprints which has become common practice (Day, 2004). In the process, latent fingerprints, which may contain trace contamination are treated with cyanoacrylate in a closed cell. As a result, a thin layer of cyanoacrylate polymer will develop along the ridges creating a cast of the fingerprint as a result of its high affinity to the amino acids, fatty acids and proteins found in fingerprints (PSU). The end result is white, understandable, and through multiple treatments can show minute details (Bumbrah, 2017). In this way, latent fingerprints can be photographed and lifted to test. As known, latent fingerprints are made up of sweat and oil; and sweat can easily evaporate. Fumigation is a means of developing older, latent fingerprints which can be photographed (Bumbrah, 2017). As the fingerprint is developed chemically and requires minimal human interaction for the process to occur, one may obtain latent fingerprints from reflective surfaces, uneven surfaces, or porous surfaces such as knives, untreated wood, and dead bodies respectively (PSU). As fingerprints are deposited on any surface which has been touched, it is important to have a large repertoire of methods to extract said prints.
Using lifting tape is a classical practice to lift fingerprints. A contrasting powder, such as Swedish soot is dusted over a fingerprint and an adhesive tape is used to lift the dusted print off a surface (Trapecar). Human skin is one of the most difficult surfaces to remove fingerprints from as fatty acids are found on both the fingerprints and on the human skin (Trapecar). Swedish soot is an agent which can visually enhance latent prints. Lifting tape is then used and the fingerprint is then placed on a white backing. Often times, high resolution images are taken to store in databases.
Overall, the collection of fingerprints inevitably leads to high resolution imaging. Cyanoacrylate and Swedish soot are two of many ways to convert latent prints into visible prints which can be photographed. Analyzers assess the prints to draw comparisons. Often times, the prints left at the scene of the crime are compared side-by-side to the victim’s, those from people of interest, and even those stored in large databases. IAFAS is the largest fingerprint database and holds more that 72 million sets of fingerprints (NFSTC). Overall, these comparisons are simple, comparing one set to another. Oftentimes, results may return inconclusive due to a poor quality sample or dissimilar features (NFSTC). The aim of developments in this field is to minimize the number of times which results return inconclusive and to minimize the amount of times in which false positives and false negatives are concluded.
Infrared spectroscopy is an analytical method that shines infrared light on a sample. The light can energize the various constituents of a molecule a specific wavenumbers (chem libretext). It can measure the amount of atoms vibrating in a sample at specific wavenumbers (which is directly proportional to the frequency of the wave) to give further insight as to the functional groups present in a molecule. In theory, two bonded atoms in a molecule can be compared to two masses on a massless spring. Hooke's law directly links the length of a spring to the amount of force applied (BBC). At the molecular level, other factors aside from the harmonic oscillation are considered such as anharmonic oscillator, coupling and the rigid rotor of more complex molecules. The anharmonic oscillator is the deviation away from the harmonic oscillation, which modifies the energy profile of the molecule. At low temperatures or low energy, the deviation from the harmonic oscillation is minimal, but as energy is added, such as the energy added from the infrared light, the energy profile is altered.
There are many ways the atoms in a molecule can vibrate (chem libretext). Stretching (which can be coupled with other atoms in or out of sync) are the basic examples of vibrational modes. There are more interesting modes such as scissoring, rocking, and wagging. The number of ways molecules are able to vibrate are dependent on whether the molecule is generally linear or not. For the most part, linear molecules have more degrees of freedom than their non linear counterparts (Chem libretext). The Fourier transform is a mathematical function that can be used to show the different parts of a continuous signal. With respect to Infrared spectroscopy, FTIR exposes a sample to different wavelengths and measures which wavelengths are absorbed. It overall has made the structural analysis of molecules much easier by dividing bands into key components one can analyze to hypothesize functional groups present in a molecule. Attenuated total reflectance, or the ATR enables solid or liquid samples to be examined with minimal preparation by collecting a series of beams. RSC best defines FTIR-ATR as:
A type of spectroscopy where infrared light is introduced into a prism at an angle
exceeding the critical angle for internal reflection. This produces an evanescent wave at
the reflecting surface (a surface which is transparent to infrared such as thallium bromide) on which the sample is supported. The distortion of the evanescent wave by the sample is measured producing a spectrum which is then subject to a Fourier transform.
The use of IR has became popularized in the last few decades. Williams et. al. were able to identify sebaceous material as well as differentiate between the prints of adults and children. An important thing to note: infrared light, and more importantly, infrared spectroscopy does not damage a fingerprint sample.As stated by Williams et. al, “the method holds promise for probing the difference between adults and children”.The research being performed here aims to further define the chemical makeup of both latent fingerprints and any solid or liquid contaminants by making use of FTIR-ATR. Objectively defining the identity of the contaminant on the fingerprint can further communicate to a forensic scientist more information about the events leading up to the time in which the fingerprint were deposited. To examine the residues of external contaminants on fingerprints, IR can identify the functional groups present on residues in order to give insight as to what is present. With reasonable logic, one may deduce what is present. Subtracting the IR graph of sebaceous excrement has been able to help but not give accurate spectra of residues which contaminate deposited fingerprints. The importance of developing new techniques to examine fingerprints gives rise to new independent test which can minimize analytical and comparative error. The use of IR is beneficial as it gives an objective way of identifying fingerprints without damaging a sample. The multiple types of methods use to lift fingerprints are important to understand as each fits a specific set of niches.
Specific Aims
Currently, there are not many ways to compare fingerprints objectively. Forensic analyst compare two images of fingerprints in order to determine whether or not the prints are a match. Oftentimes, results come up inconclusive due to the subpar quality of the print collected. Even worse, they may draw an incorrect conclusion. Currently, research has been conducted to analyze fingerprints without damaging them. It is known that infrared spectroscopy (IR) does not damage prints and can determine functional groups present in the residue of fingerprints.
It is known that the fingerprints one was born with will not change in their lifetime. It is also known that there are three types of prints which can be left behind. It is easy to physically compare to clear contrasting images made by patent prints while it is more difficult to even see latent prints. There are many lifting techniques used: and the best one is selected by looking at the surface the print is lifted from, whether or not it is visible and the resources one has to lift them. Swedish soot is a black dust used to make latent print visible; superglue fuming is used to lift prints on uneven surfaces or to keep contaminants intact.
Overall, the use of IR aims to create a new property in which forensic analyst can use to help further compare fingerprints. Determining the residue can help further determine the identity of the person who left the fingerprint behind. With more research, one may be able to determine that someone has an addiction based off the residue on fingerprints; a person who doesn’t take aspirin shouldn’t have aspirin on their fingers. Similarly, this can be applied to many molecules such as cocaine.
First, one must be able to confirm that IR spectroscopy can be individualized based on residue present. It should work as peer-reviewed literature has stated that it is possible. It is also interesting to note that this can be confirmed theoretically by noting that there are organic molecules present. ATR- IR allows for solid or liquid samples to be analyzed with little prep. Therefore, theoretically it is possible to get an IR spec from a fingerprint. Since diet is a major contributor to what is secreted, one may logically hypothesize that diet will also impact the wavefunction giving more individualized readings from the instrument. Next, one must be able to read the sample without having the results skewed by the lifting technique. The cyanoacrylate will most likely skew results but the swedish soot may not because of the bonds. Other organic samples may also skew the results. However, I believe metallic based lifting powders will not skew the data as the metal atoms are too heavy to appear on the IR graph. Finally, one should be able to distinguish residues. This might be difficult as some functional groups are fairly common. Ideally, an IR spec will be paired with another test to get more definite result. I believe that residues may be distinguished based off of standards and the functional groups present. However, more independent test or deductive logic may be necessary to identify residues.
Innovation
The research being conducted can give more subjective information about fingerprints overall. It can be adapted into the health field to determine whether or not one has been on illicit substances. It can be further developed in the forensic field to increase the accuracy and precision of results. That will lead to more accurate arrest which can be objectively considered a way to better society. From the sociological perspective, it can be used to track the use of illicit substances in areas.
Furthermore, development in this field will increase the popularity of the instruments used. With conclusive data, it can further change the way fingerprints are systematically stored. As noted, the way fingerprints are currently analyzed and stored has not changed much since the 20th century. Development in this field will make the lives of forensic analyst better by giving them more ways to compare fingerprints.
At this time, subtracting spectra show that the residue on fingerprints can be isolated to determine the IR spectra of the residue alone. This can be compared to a standard to determine the identity of an unknown reside. It does not matter whether or not an excessive amount of unknown contaminating residue was directly added to the fingerprint or if it was picked up by the environment; both give the same resulting spectra.
Research method
Up to this point, fingerprints were set up with arbitrary amounts of aspirin. In the first trial, the stand was created by placing pure aspirin on the ATR attachment of the IR and taking the spectra. Fingerprint samples were set up in 4 different ways:
The first way was the easiest. A blank fingerprint was placed directly on the cleaned IR. In between trials, the stage was cleaned with acetone and a clean lens wipe. Next a fingerprint that had non-visible amounts of aspirin was placed directly onto the stage.This was done by first placing aspirin directly on the finger and brushing off residue.There were 4 repeated trials in this set to ensure precision.
The next set was performed similarly, except these fingerprints were lifted. The lifting tape was common packing tape. A blank fingerprint was lifted. Two different types of aspirin prints were lifted. In one scenario, aspirin was on the fingerprint, then the fingerprint was deposited on a clean surface, to then be lifted. In the second scenario, there was aspirin on a clean and a fingerprint was placed on top of the aspirin then the fingerprint was lifted. In both scenarios, the results came out the same.
[Data was removed as blackboard said the file was too large; will be emailed to Ed]
Intended future procedure:
Determining whether or not I can identify “trace amounts” of aspirin
First, I would like to determine whether or not I can detect micro-molar (“trace”) amounts of aspirin on the FTDR attachment. For that, I’ve decided to set up a procedure using Micromolar solutions of aspirin in smaller aliquots and drop it onto a glass slide. Ideally, I create a 5mL solution drop and undergo the assumption that solution is completely homogenous to determine what is the smallest degree I can find.
However, common analytical balances can only assure one to the .001 g with some degree of accuracy; therefore, calculating a 5mL solution which such a small concentration does not work. Instead, I’ve decided to make one large stock solution and dilute it into 5mL aliquots.
First, I decided to make a 1L 100 micro-molar solution by putting .01801 g of aspirin into a 1L solution. Then I will dilute that 100 micro-molar solution into 5. mL samples by making larger 20. mL solutions.
Each mL of the original solution should contain .099 moles of aspirin.
Diluting that 1. mL with 99mL of water gives us a working solution of 1 micro-molar.
Diluting another 1. mL with 49mL DI gives us a working solution of 2 micro-molar.
Diluting 2 mL with 49mL of DI gives us a working solution of 4 micro-molar.
Diluting 3mL with 49mL of DI gives us 6 micro-molar solution; 4mL becomes 8uM and 5mL becomes 10 uM.
With this, I plant to put a drop onto a slide and determine whether or not I can find the difference and how. I plan to note degrees of %T difference compared to a standard (100 uM solution and negative control). If after a few trials, I can determine a clear trend to not only see aspirin at the micro-molar concentration, but also how much, I move on to the next part.
Molar mass of aspirin: 180.157 g/mol
Determining whether or not this can be traced on a fingerprint
By pouring 1 drop of water onto the slide after placing my fingerprint, I am hoping to detect both my fingerprint and the micro-molar concentration. This follows the procedure I have been doing with the pure powder, but now controlled with a working concentration.
Conclusion
Here, the use of attenuated total reflectance infrared spectroscopy to analyze latent, lifted fingerprints is examined. New ways to further differentiate between fingerprints will help further facilitate social justice by improving the way forensic analyst analyze fingerprints. There has been little change in how fingerprints are analyzed since the 20th century. Here, the use of FTIR-ATR is used to determine whether aspirin can be detected in sample fingerprint in various situations. It is helpful in identifying contaminants on a fingerprint and does not damage the sample, which are two benefits. With more information on the importance of the fingerprint region on the IR spectra, (the right side of the spectra; less than 1600 wavenumbers), one may be able to make use of IR as a formal way to analyze fingerprints.
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