Efficacy and stability of a nitrogen-doped carbon dot nanocomposite for revealing aged latent fingerprints on glass surfaces

Fingerprint detection has been a cornerstone to criminal investigations. The traditional methods for latent fingerprint detection have drawbacks like limited contrast, sensitivity, selectivity, and potentially erasing fingerprint details. Also, latent fingerprint preservation plays a crucial role in forensic investigations. However, older fingerprints pose a significant challenge in casework. This study aimed to assess the effectiveness of a synthesized nitrogen-doped carbon dot (NC-dot) nanocomposite in visualizing latent fingerprints on glass surface across different intervals and its durability and stability on the developed print. Nitrogen-doped carbon dots were synthesized via microwave irradiation of citric acid and ethylenediamine, whereas graphitic carbon nitride was produced from urea. A g-C₃N₄/NC dot nanocomposite was synthesized using mixing and ultrasonication. Ninety-nine latent fingerprint samples were obtained on glass slides and classified as fresh, one month old, and three months old. Subsequent to initial development, all samples were maintained for a duration of two months and thereafter re-examined. Fingerprints were treated with nanocomposite powder, examined under UV light (312 nm), and assessed by specialists for ridge details, contrast, and identifiability by minutiae analysis. Fingerprints were categorized into three development groups: fresh, one month, and three months. Friction ridge detail development, contrast quality, and identification accuracy were assessed. Results revealed that fresh fingerprints demonstrated significantly the highest ridge detail development and contrast, with a substantial portion (87.9%) showing full or near-full ridge detail. Fingerprint identification rates declined over time, with fresh samples achieving 93.9% identifiability, one-month-old samples at 51.5%, and three-month-old samples at 27.3%. Despite the natural degradation over time, a substantial proportion of three-month-old fingerprints retained identifiable ridge details, enabling partial identification. The study highlighted the promising role of synthesized (NC-dot) nanocomposite in enhancing aged latent fingerprint recovery.