Forensic science is an interdisciplinary field that applies scientific principles to legal investigations, playing a vital role in the identification of individuals and the reconstruction of criminal events.¹ Personal identification remains one of the most important objectives in forensic investigations, particularly in cases involving homicide, mass disasters, missing persons, and severely decomposed human remains.² Although DNA profiling has revolutionized forensic identification due to its high specificity and reliability, several practical limitations exist.³ Biological samples may become degraded through environmental exposure, heat, microbial activity, chemical contamination, or prolonged postmortem intervals, resulting in compromised DNA quality and reduced evidentiary value.^4,5 Consequently, there is a growing need for alternative and complementary forensic biomarkers that can withstand adverse conditions while retaining individual-specific characteristics.

Fingernails are highly resilient biological structures composed predominantly of keratin, a fibrous protein rich in sulfur-containing amino acids.^6,7 Unlike soft tissues, fingernails exhibit remarkable resistance to physical, chemical, and biological degradation, allowing them to persist long after other biological materials have deteriorated^.8,9 Their durability makes them particularly valuable in forensic investigations involving burned bodies, skeletal remains, and advanced decomposition.¹⁰ In addition to structural proteins, fingernails contain various biochemical constituents, including amino acids, peptides, and trace elements, which may reflect an individual's genetic makeup, dietary habits, metabolic status, environmental exposures, and lifestyle factors.¹¹

Recent advances in forensic biochemistry and analytical technologies have opened new opportunities for the examination of nail-derived biomarkers.¹² Techniques such as high-performance liquid chromatography (HPLC), mass spectrometry, and atomic absorption spectrophotometry enable accurate quantification of keratin degradation products and trace elemental concentrations from small nail samples. Variations in compounds such as cysteine, cystine, methionine, and keratin-associated peptides, together with elemental profiles including zinc, calcium, iron, copper, and magnesium, may generate distinctive biochemical patterns capable of differentiating individuals.¹³ These biochemical signatures have the potential to complement conventional forensic methods and enhance identification accuracy when DNA or fingerprint evidence is unavailable or inconclusive.

The concept of biochemical fingerprinting has gained increasing attention in forensic research because it provides information beyond traditional genetic analysis. Unlike DNA profiling, which primarily focuses on genetic identity, biochemical profiling may also capture environmental and physiological influences unique to each individual.^14,15 Such information could prove valuable in forensic casework, disaster victim identification, and the analysis of fragmented biological remains. Moreover, the collection of fingernail samples is simple, non-invasive, cost-effective, and feasible in both living and deceased individuals.

Therefore, the present study was designed to investigate the forensic applicability of fingernail keratin degradation products and trace elemental composition as potential biomarkers for human identification. By analyzing fingernail samples collected from 80 volunteers, this study aims to evaluate inter-individual biochemical variability and determine the accuracy of nail-based biochemical profiling as a supplementary tool in forensic investigations. The findings may contribute to the development of novel forensic identification strategies and expand the role of biochemical evidence in modern forensic science.

Study Design and Setting A cross-sectional analytical forensic study was conducted to evaluate the potential of fingernail keratin degradation products and trace elemental composition as biomarkers for human identification. The study was carried out in the Biochemistry and Forensic Sciences Research Laboratory over a period of six months. Study Population A total of 80 healthy volunteers were recruited for the study, comprising 40 males and 40 females aged between 18 and 60 years. Participants were selected through convenience sampling after obtaining informed consent. Inclusion Criteria • Healthy individuals aged 18–60 years. • Individuals willing to provide fingernail samples. • Participants without visible nail abnormalities. Exclusion Criteria • Individuals with fungal or bacterial nail infections. • Participants with chronic dermatological disorders affecting nails. • Individuals receiving chemotherapy or long-term medication known to alter nail composition. • Subjects with recent nail cosmetic treatments such as artificial nails or gel coatings. Sample Collection Fingernail clippings were collected from all ten fingers using sterile stainless-steel nail clippers. Approximately 100–150 mg of nail material was obtained from each participant. Samples were placed in labeled sterile polypropylene containers and transported to the laboratory for analysis. Prior to biochemical assessment, nail samples were washed with distilled water followed by 70% ethanol to remove external contaminants and allowed to air dry. Preparation of Nail Extracts The cleaned nail samples were finely powdered using a laboratory grinder. Approximately 50 mg of powdered nail material was hydrolyzed in 6N hydrochloric acid at 110°C for 24 hours. The hydrolysates were filtered and diluted with phosphate-buffered saline for biochemical analyses. Analysis of Keratin Degradation Products Levels of keratin degradation products, including cysteine, cystine, methionine, and keratin-associated peptides, were quantified using High-Performance Liquid Chromatography (HPLC). Standard calibration curves were prepared for each analyte, and concentrations were expressed as µmol/g of nail tissue. Trace Element Analysis The concentrations of zinc (Zn), calcium (Ca), iron (Fe), copper (Cu), and magnesium (Mg) were determined using Atomic Absorption Spectrophotometry (AAS). Nail samples underwent acid digestion with nitric acid and perchloric acid prior to elemental analysis. Results were expressed as µg/g of nail tissue. Quality Control All analyses were performed in triplicate to ensure reproducibility. Certified reference standards and blank samples were included in each analytical batch. Instruments were calibrated daily according to manufacturer recommendations. Statistical Analysis Data were analyzed using SPSS version 26.0. Results were expressed as mean ± standard deviation (SD). Differences in biochemical parameters among participants were assessed using one-way analysis of variance (ANOVA). Pearson correlation analysis was used to evaluate associations between keratin degradation products and trace elements. Discriminant function analysis was performed to determine the accuracy of biochemical profiling for individual identification. A p-value < 0.05 was considered statistically significant.

A total of 80 fingernail samples were successfully collected and analyzed. Significant inter-individual variability was observed in both keratin degradation products and trace elemental composition. The concentrations of sulfur-containing amino acids and keratin-associated peptides varied considerably among participants, suggesting the presence of unique biochemical signatures. Similarly, trace element analysis demonstrated measurable differences in elemental profiles between individuals. Statistical analysis revealed that several biochemical parameters possessed strong discriminatory power for forensic identification. The combination of keratin degradation products and trace elemental composition provided the highest identification accuracy.

Table 1. Concentration of Keratin Degradation Products in Fingernail Samples (n = 80)

P-value: <0.001 for inter-individual variation.

Table 2. Trace Element Composition of Fingernail Samples (n = 80)

P-value: <0.001 for inter-individual variation.

Table 3. Forensic Identification Accuracy Based on Biochemical Profiling

P-value: <0.001.

The present study evaluated the forensic potential of fingernail keratin degradation products and trace elemental composition as biomarkers for human identification. The findings demonstrated significant inter-individual variability in both biochemical and elemental profiles, supporting the hypothesis that fingernails possess unique molecular characteristics that may be useful in forensic investigations. Since fingernails are highly resistant to environmental degradation, they represent a valuable source of biological information when conventional forensic evidence such as blood, soft tissue, or DNA is unavailable or compromised.

Among the keratin degradation products analyzed, cysteine and cystine exhibited the greatest discriminatory power. These sulfur-containing amino acids are major structural components of keratin and contribute to the formation of disulfide bonds that determine nail strength and stability. Variations in their concentrations may reflect differences in genetic background, protein metabolism, nutritional status, and environmental influences. The observed variability among participants suggests that keratin-associated biochemical signatures could serve as individual-specific markers for forensic identification.

Trace element analysis further revealed substantial differences in the concentrations of zinc, calcium, iron, copper, and magnesium among participants. These elements are incorporated into nail tissue over time and may be influenced by dietary intake, occupational exposure, environmental conditions, and physiological processes. Zinc and calcium demonstrated the highest variability, indicating their potential usefulness in distinguishing individuals. Because elemental profiles remain relatively stable after nail formation, they may provide supplementary forensic information even in degraded specimens.

The combined use of keratin degradation products and trace elemental composition achieved the highest identification accuracy (92.5%), outperforming either biomarker category alone. This finding highlights the advantage of a multi-marker forensic approach, where biochemical and elemental characteristics collectively create a more comprehensive and individualized profile. Such an approach may enhance forensic investigations involving fragmented remains, disaster victim identification, mass casualty incidents, and cases where traditional DNA analysis is unsuccessful.

A notable strength of this study is the use of non-invasive, durable, and easily collectible biological material. Fingernail samples require minimal storage conditions, are less susceptible to contamination than other biological specimens, and can persist under harsh environmental circumstances. These properties make them particularly attractive for forensic applications. However, the study was limited by its relatively small sample size and single-center design. Future studies involving larger and more diverse populations, as well as advanced analytical techniques such as mass spectrometry-based metabolomics and proteomics, may further improve the discriminatory capacity and forensic applicability of nail-based biochemical profiling.

Overall, the findings suggest that fingernail keratin degradation products and trace elemental signatures possess considerable potential as supplementary forensic biomarkers. Their integration into forensic practice may strengthen personal identification procedures and provide additional evidentiary support when conventional methods are limited or unavailable.

This study demonstrates that fingernail keratin degradation products and trace elemental composition possess significant potential as supplementary biomarkers for forensic human identification. The observed inter-individual variability and high identification accuracy achieved through combined biochemical profiling indicate that fingernails can provide reliable forensic information, particularly when conventional DNA evidence is degraded or unavailable. These findings support the incorporation of nail-based biochemical analysis into forensic investigations and encourage further large-scale studies to validate its practical application.

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