Chasing criminals with chitosan

Chitosan is already being used in many ways in the pharmaceutical, medical and food industries. A less explored field of application is forensics, for example to make fingerprints visible. In the following article we would like to present a study in which the unique properties of chitosan coupled with lysine are used as a powder to visualize latent fingerprints on glass and rubber surfaces.

NOVEL CHITOSAN/TRIPOLYPHOSPHATE/L-LYSINE CONJUGATES FOR THE DETECTION AND ENHANCEMENT OF LATENT FINGERPRINTS

A novel chitosan/tripolyphosphate/L-lysine conjugates for latent fingerprints detection and enhancement. Vučković, N.; Glođović, N.; Radovanović, Ž.; Janaćković, Đ.; Milašinović, N., J Forensic Sci. 2021 Jan;66(1):149-160. https://doi.org/10.1111/1556-4029.14569

The arrangement of grooves and furrows on the surface of the finger are unique to each individual. For this reason, fingerprints remain an important physical evidence tool when it comes to solving crimes. There are three types of fingerprints used in forensics: the visible, patent fingerprint, the plastic fingerprint, and the non-visible, latent fingerprint.

Latent fingerprints are secreted on surfaces and consist of a mixture of sebum, sweat, and apocrine secretions. To make them visible, various dyes and powders are applied in forensics. However, these substances are often toxic when inhaled, which is why biopolymers, such as chitosan, are currently being increasingly investigated for visualizing fingerprints.

Chitosan is of particular interest because its structure and polycationic charge enable it to bind latent fingerprint fluids through electrostatic and lipophilic interactions. In addition to chitosan, lysine can also interact with components from secreted sweat e.g. calcium ions, amino acids and lipids. For the reason, in the presented study, chitosan and lysine were coupled via sodium tripolyphosphate (TPP) and their application as a powder to detect and enhance latent fingerprints was investigated. Chitosan coupled with TPP (6:1 and 1:1 ratio) and chitosan coupled with TPP and lysine (6:1:1 and 1:1:1 ratio) were compared on rubbery surface and glass. BVDA Magnetic Silver Powder, which is commonly used in forensics, served as a reference.

RESULTS

• the chitosan-TPP-lysine powders were easier to grind and had a finer structure than the chitosan-TPP powders
• on the rubber surface only results for tallow fingerprints were observable
• no detection was possible for dry fingerprints
• a significantly better visualization of fingerprints was observed on the glass surface
• acceptable results for chitosan-TPP powder, but significantly improved in chitosan-lysine conjugates→ results of chitosan-TPP-lysine 6:1:1 were comparable to BVDA Magnetic Silver Powder
• Improved visualization with increased chitosan content
• Better visualization of fingerprints after storage under humid rather than dry conditions
• Good images with chitosan-TPP-lysine 6:1:1 even after 3 and 6 months of moist storage, respectively

Conclusions: The study demonstrated the potential of chitosan-TPP-lysine conjugates for latent fingerprint detection and enhancement. The different powders were able to bind sweat and sebum of the prints via lipophilic and electrostatic interactions, making them visible. It was found that chitosan-TPP-lysine conjugates showed better results than those without lysine. Due to the non-toxic nature of biopolymer-based powders, in the future the working environment for forensic scientists in criminal investigation could be made safer and thus more efficient. Link to article: https://onlinelibrary.wiley.com/doi/epdf/10.1111/1556-4029.14569