Metal-DNA interactions: Exploring the impact of metal ions on key stages of forensic DNA analysis.

Forensic DNA analysis continues to be hampered by the complex interactions between metals and DNA. Metal ions may cause direct DNA damage, inhibit DNA extraction and polymerase chain reaction (PCR) amplification or both. This study evaluated the impact of metal ions on DNA extraction, quantitation, and short tandem repeat profiling using cell-free and cellular (saliva) DNA. Of the 11 metals assessed, brass exhibited the strongest PCR inhibitory effects, for both custom and Quantifiler Trio quantitation assays. Metal ion inhibition varied across the two quantitative PCR assays and the amount of DNA template used. The Quantifiler Trio internal PCR control (IPC) only revealed evidence of PCR inhibition at higher metal ion concentrations, limiting the applicability of IPC as an indicator of the presence of metal inhibitor in a sample. Notably, ferrous ions were found to significantly decrease the extraction efficiency of the DNA-IQ DNA extraction system. The amount of DNA degradation and inhibition in saliva samples caused by metal ions increased with a dilution of the sample, suggesting that the saliva matrix provides protection from metal ion effects.

From clean spaces to crime scenes: Exploring trace DNA recovery from titania-coated self-cleaning substrates.

Titanium dioxide (titania, TiO2) is frequently used as a coating for a variety of self-cleaning products, such as antifogging vehicle mirrors, ceramic tiles, and glass windows because of its distinct physiochemical features. When exposed to light TiO2 causes photocatalytic decomposition of organic contaminants, potentially compromising DNA integrity. The impact of TiO2-coated commercial glasses, Bioclean® and SaniTise™, on trace DNA persistence, recovery, and profiling was investigated. DNA in saliva and touch samples deposited on self-cleaning glass slides exposed to indoor fluorescent light for up to seven days was more degraded than control samples indicating some degree of fluorescent light-induced photocatalytic activity of the self-cleaning surfaces. When exposed to sunlight, DNA yields from saliva and touch samples deposited on the titania-coated substrates decreased rapidly, with a corresponding increase in DNA degradation. After three days no DNA samples applied to self-cleaning glass and exposed to natural sunlight yielded STR profiles. These results suggest that the photocatalytic activation of TiO2 is the likely mechanism of action underlying the extreme DNA degradation on the Bioclean® and SaniTise™ glasses. Consequently, rapid sample collection and use may be warranted in casework scenarios involving TiO2-coated materials.

Quantitative PCR overestimation of DNA in samples contaminated with tin.

Metals can pose challenges while conducting forensic DNA analysis. The presence of metal ions in evidence-related DNA extracts can degrade DNA or inhibit PCR as applied to DNA quantification (real-time PCR or qPCR) and/or STR amplification, leading to low success in STR profiling. Different metal ions were spiked into 0.2 and 0.5 ng of human genomic DNA in an "inhibition study" and the impact was evaluated by qPCR using the Quantifiler™ Trio DNA Quantification Kit (Thermo Fisher Scientific) and an in-house SYBR Green assay. This study reports on a contradictory finding specific to tin (Sn) ions, which caused at least a 38,000-fold overestimation of DNA concentration when utilizing Quantifiler Trio. This was explained by the raw and multicomponent spectral plots, which indicated that Sn suppresses the Quantifiler Trio passive reference dye (Mustang Purple™, MP) at ion concentrations above 0.1 mM. This effect was not observed when DNA was quantified using SYBR Green with ROX™ as the passive reference, nor when DNA was extracted and purified prior to Quantifiler Trio. The results show that metal contaminants can interfere with qPCR-based DNA quantification in unexpected ways and may be assay dependent. The results also highlight the importance of qPCR as a quality check to determine steps for sample cleanup prior to STR amplification that may be similarly impacted by metal ions. Forensic workflows should recognize the risk of inaccurate DNA quantification of samples that are collected from substrates containing tin.

Lip print enhancement: review.

Lip print (LP) evidence can be an essential tool for human forensics. LPs have conventionally been developed using substances such as lysochrome dyes, fluorescent dyes, indigo dye, aluminium powder, and silver metallic powder. However, techniques for LP enhancement from various substrates are currently inconsistent and lack standardisation in practice. This review summarises current knowledge on the physical and chemical techniques of LP enhancement, identifies limitations, and provides suggestions for future research on practical applications of cheiloscopy as a forensic tool in criminal justice.Key pointsThe grooves and wrinkles of the human lip establish unique patterns that persist throughout life.Cheiloscopic patterns exhibit discriminatory individual characteristics that may constitute circumstantial forensic evidence.Enhancement techniques for latent lip prints on porous and nonporous substrates can be classified as physical or chemical.Unlike fingerprint, there is a current lack of consistency and/or standardisation on latent lip print enhancement methods in frontline forensic practice.