Role of molecular diagnostics in forensic science

AI-driven feature selection and epigenetic pattern analysis: A screening strategy of CpGs validated by pyrosequencing for body fluid identification

Identification of body fluid stain at crime scene is one of the important tasks of forensic evidence analysis. Currently, body fluid-specific CpGs detected by DNA methylation microarray screening, have been widely studied for forensic body fluid identification. However, some CpGs have limited ability to distinguish certain body fluid types. The ongoing need is to discover novel methylation markers and fully validate them to enhance their evidentiary strength in complex forensic scenarios. This research gathered forensic-related DNA methylation microarrays data from the Gene Expression Omnibus (GEO) database. A novel screening strategy for marker selection was developed, combining feature selection algorithms (elastic net, information gain ratio, feature importance based on Random Forest, and mutual information coefficient) with epigenetic pattern analysis, to identify CpG markers for body fluid identification. The selected CpGs were validated through pyrosequencing on peripheral blood, saliva, semen, vaginal secretions, and menstrual blood samples, and machine learning classification models were constructed based on the sequencing results. Pyrosequencing results revealed 14 CpGs with high specificity in five types of body fluid samples. A machine learning classification model, developed based on the pyrosequencing results, could effectively distinguish five types of body fluid samples, achieving 100 % accuracy on the test set. Utilizing six CpG markers, it was also feasible to attain ideal efficacy in identifying body fluid stains. Our research proposes a systematic and scientific strategy for screening body fluid-specific CpGs, contributing new insights and methods to forensic body fluid identification.

Convergence of Surface-Enhanced Raman Scattering with Molecular Diagnostics: A Perspective on Future Directions

Molecular diagnostics (MD) is widely employed in multiple scientific disciplines, such as oncology, pathogen detection, forensic investigations, and the pharmaceutical industry. Techniques such as polymerase chain reaction (PCR) revolutionized the rapid and accurate identification of nucleic acids (DNA, RNA). More recently, CRISPR and its CRISPR-associated protein (Cas) have been a ground-breaking discovery that is the latest revolution in molecular biology, including MD. Surface-enhanced Raman scattering (SERS) is a very attractive alternative to fluorescence as the currently most widely used optical readout in MD. In this Perspective, milestones in the development of MD, SERS-PCR, and next-generation approaches to MD, such as Specific High-Sensitivity Enzymatic Reporter UnLOCKing (SHERLOCK) and DNA Endonuclease-Targeted CRISPR Trans Reporter (DETECTR), are briefly summarized. Our perspective on the future convergence of SERS with MD is focused on SERS-based CRISPR/Cas (SERS-CRISPR) since we anticipate many promising applications in this rapidly emerging field. We predict that major future developments will exploit the advantages of real-time monitoring with the superior brightness, photostability, and spectral multiplexing potential of SERS nanotags in an automated workflow for rapid assays under isothermal, amplification-free conditions.

PCR Technologies for Point of Care Testing: Progress and Perspectives

Since the Human Genome Project completed in 2000, the sequencing of the first genome, massive progress has been made by medical science in the early diagnosis and personalized therapies based on nucleic acids (NA) analysis. To allow the extensive use of these molecular methods in medical practice, scientific research is nowadays strongly focusing on the development of new miniaturized and easy-to-use technologies and devices allowing fast and low cost NA analysis in decentralized environments. It is now the era of so-called genetic "Point-of-Care" (PoC). These systems must integrate and automate all steps necessary for molecular analysis such as sample preparation (extraction and purification of NA) and detection based on PCR (Polymerase Chain Reaction) technology in order to perform, by unskilled personnel, in vitro genetic analysis near the patient (in hospital, in the physician office, clinic, or home), with rapid answers and low cost. In this review, the recent advances in genetic PoC technologies are discussed, including the extraction and PCR amplification chemistry suitable for PoC use and the new frontiers of research in this field.

A modifiable microarray-based universal sensor: providing sample-to-results automation

A microfluidic system consisting of generic single use cartridges which interface with a workstation allows the automatic performance of all necessary sample preparation, PCR analysis and interpretation of multiplex PCR assays. The cartridges contain a DNA array with 20 different 16mer DNA “universal” probes immobilized at defined locations. PCR amplicons can be detected via hybridization of user-defined “reporter” probes that are complementary at their 3′ termini to one or more of the universal probes and complementary to the target amplicons at their 5′ termini. The system was able to detect single-plex and multiplex PCR amplicons from various infectious agents as well as wild type and mutant alleles of single nucleotide polymorphisms. The system's ease of use was further demonstrated by converting a published PCR assay for the detection of Mycobacterium genitalium in a fully automated manner. Excellent correlation between traditional manual methods and the automated analysis performed by the workstation suggests that the system can provide a means to easily design and implement a variety of customized PCR-based assays. The system will be useful to researchers or clinical investigators seeking to develop their own user defined assays. As the U.S. FDA continues to pursue regulatory oversight of LDTs, the system would also allow labs to continue to develop compliant assays.

Shotgun metagenomics of biological stains using ultra-deep DNA sequencing

A detailed molecular analysis of blood or other biological stains at a crime scene is often hampered by the low quantity and quality of the extractable DNA. However, the determination of the origin and composition of a stain is in most cases a prerequisite for the final elucidation of a criminal case. Standard methodologies, e.g. amplification of DNA followed by microsatellite typing or mitochondrial DNA sequencing, are often not sensitive enough to result in sufficient and conclusive data. We have applied ultra-deep DNA sequencing using the 454 pyrosequencing technology on a whole genome amplified (WGA) environmental biological stain, which was analysed unsuccessfully with standard methodologies following WGA. With the combination of WGA and 454 pyrosequencing, however, we were able to generate 7242 single sequences with an average length of 195bp. A total of 1,441,971bp DNA sequences were generated and compared with public DNA sequence databases. Using RepeatMasker and basic logical alignment search tool (BLAST) searches against known microbial and mammalian genomes it was possible to determine the metagenomic composition of the stain, i.e. 4.2% bacterial DNA, 0.3% viral DNA, 2.7% fungal DNA, 10.3% mammalian repetitive DNA, 0.9% porcine DNA, 0.13% human DNA and 81.5% DNA of unknown origin. Our data demonstrate that 454 pyrosequencing has the potential to become a powerful tool not only in basic research but also in the metagenomic analysis of biological trace materials for forensic genetics.

DNA Fingerprinting in the Criminal Justice System: An Overview

DNA fingerprinting is a powerful technology that has revolutionized forensic science. No two individuals can have an identical DNA pattern except identical twins. Such DNA-based technologies have enormous social implications and can help in the fight against crime. This technology has experienced many changes over time with many advancements occurring. DNA testing is a matter of serious concern as it involves ethical issues. This article describes various trends in DNA fingerprinting and the current technology used in DNA profiling, possible uses and misuses of DNA databanks and ethical issues involved in DNA testing. Limitations and problems prevailing in this field are highlighted.