project

Team UCalgary BIOMOD 2018

Motivation Fingerprints have been known as unique identifiers for centuries – in 247 BCE the first emperor of the unified Chinese empire, Qin Shi Huang, used his fingerprint on clay to seal the documents. Later, fingerprints earned a place in palmistry and fortune telling. Whorl patterns were believed to bring happiness, loops, on the other hand, disaster (Figure 1) ﷯ Figure 1. Three distinct fingerprint patterns: arch, whorl, and loop (left to right) In Europe, fingerprints were first used for identification of criminals at the beginning of the 20th century with New Scotland Yard adopting the fingerprint technology in 1901. Not all police departments were so enthusiastic about fingerprint analysis, however. In 1911, the world was shocked by the news that the Mona Lisa had been stolen from the Louvre. ﷯ Figure 2: The Mona Lisa The painting that had once decorated the bedroom of Napoleon Bonaparte was eventually discovered to be in the hands of a petty criminal named Vincenzo Peruggia. During the theft, Peruggia had generously left his fingerprints on the glass that covered the painting. However, none of the 60 detectives who were involved in the crime scene investigation followed up on the lead, despite knowing that the Parisian police already had a fingerprint database (which actually included Peruggia’s prints as well!). As a result, the crime often described as the greatest art theft of the 20th century was not resolved for two years. Fingerprinting became a universal method for identifying criminals in France only three years after this heist, in 1914. All the Parisian detectives had to do was to compare two fingerprint patterns – one in the database with the one that was left behind by Peruggia – in order to discover the thief. However, it is not always so easy. Identification is only possible if the fingerprint of a suspect is in the police database. What if it is not? Is there more hidden information in a fingerprint than just a unique pattern? Would it be possible for law enforcement agencies to develop a fingerprint and obtain information on biological gender, age, drug abuse, predisposition to certain diseases, etc. of an individual who left the print behind, thus, reducing the circle of suspects and accelerating the investigation? This research question became a project theme of the UofC BioMod team this year. “Latent” fingerprints – those left behind on surfaces that have been touched – are mainly composed of a residue of sweat and skin oils. With current forensic technology, there are 3 major techniques in developing latent prints: dusting, cyanoacrylate fuming, and ninhydrin staining. Dusting involves gently distributing aluminum powder onto a surface with potential prints. Dust adheres to the moisture and oils present in the print, making it more visible. ﷯ Figure 3: Latent fingerprint visualized using dusting. In cyanoacrylate fuming, an object is placed into a closed container with a dish of heated cyanoacrylate. As the cyanoacrylate vaporizes, it deposits on surfaces inside the container. The moisture in the latent prints accelerates polymerization of the cyanoacrylate on the fingerprint, revealing the prints as white patterns on the surface (Figure 4). ﷯ Figure 4: Latent prints being visualized using cyanoacrylate fuming. Ninhydrin staining relies on the reaction of the colorless compound ninhydrin with amine groups found on the proteins in sweat. The reaction results in a purple-colored product that makes the fingerprint pattern visible. The techniques described above only allow one to develop the fingerprint pattern, which can be done well and reliably nowadays. In this project, we aim to design a method that would provide law enforcement agencies with the ability not just to visualize fingerprints but also obtain information on other biological traits of a culprit. Our general approach to enhancing the capabilities of fingerprint analysis lies in identifying different biomarkers within sweat and then targeting these biomarkers in fingerprints by labelling them with highly luminescent nanoparticles. To test if this idea works as a proof of principle, for this project, we selected lysozyme as a biomarker for labelling. This protein is known to be the most abundant compound in human sweat. Discovered in 1923 by Alexander Fleming, this enzyme is found in a wide variety of species. It acts as an antimicrobial agent capable of catalyzing the hydrolysis of certain linkages in the cell walls of bacteria. Lysozyme contains 129 amino acids and is a single polypeptide chain that folds into a compact structure with a cleft along the proteins surface. How our method works: The core component of our ink for fingerprint development is nanoparticles made of cadmium telluride core (CdTe) and cadmium sulfide (CdS) shell. These luminescent particles are known as quantum dots (QDs). When excited with UV light, they emit visible light due to effect known as quantum confinement. During synthesis, these nanoparticles were functionalized with aptamers – single stranded oligonucleotides that bind strongly to specific molecular targets. In our project, lysozyme specific aptamers have been used to bind nanoparticles to the lysozyme present in fingerprints. Upon completing the quantum dot synthesis and confirming that lysozyme specific aptamers are immobilized on the nanoparticle surface, using our ink we successfully developed several patterns on glass surfaces that contained lysozyme. To confirm that the aptamer functionality is preserved upon immobilization on the nanoparticle surface, we first developed a bear-paw pattern that was hand drawn on a glass using a solution of lysozyme at a concentration of 10mg/mL (Figure 5). The large area exposed to lysozyme in this pattern made visualization easier to test the conditions needed for binding. ﷯ Figure 5. Visualization of patterns with aptamer functionalized QDs. LEFT: a bear-paw pattern was drawn on the slide using a lysozyme solution and incubated with a solution of the aptamer-functionalized QDs. After rinsing, the pattern is visible under UV irradiation. RIGHT: the same pattern was drawn with the lysozyme solution and incubated with unmodified QDs (no aptamer). After rinsing, no specific binding to the lysozyme pattern is seen with UV irradiation Next, a latent fingerprint was created on an epoxy functionalized glass slide. The print was made by rubbing a fingertip against the forehead first, and then pressing the fingertip tightly against the glass surface. The created fingerprints were incubated with aptamer functionalized quantum dots and bare quantum dots as a control. The results are presented in Figure 6. ﷯ Figure 6. Epoxy-coated glass slides with latent fingerprints. LEFT: fingerprint was incubated with a solution of the aptamer-functionalized QDs. RIGHT: fingerprint was incubated with a solution of non-modified QDs (no aptamer). After rinsing with water and viewing under UV light, binding of the QDs to the fingerprint pattern is visible only with the aptamer-modified QDs. SUMMARY Our team has successfully developed and tested a method for visualizing specific biomarkers in latent fingerprints. We have shown that by using aptamer-functionalized quantum dots, luminescent particles can be bound to specifically targeted molecules of interest in a fingerprint, providing information about the composition of the sweat and skin oils in the print that may be linked to biological traits. Lysozyme was used as a proof of concept in this study, but simply by incorporating a different aptamer onto the quantum dot surface during synthesis, any molecule of interest could be targeted.