DNA sequencing, starting with Sanger's chain termination method in 1977 and evolving into the next generation sequencing (NGS) techniques of today that employ massively parallel sequencing (MPS), has become essential in application areas such as biotechnology, virology, and medical diagnostics. Reflected by the growing number of articles published over the last 2–3 years, these techniques have also gained attention in the forensic field. This review contains a brief description of first, second, and third generation sequencing techniques, and focuses on the recent developments in human DNA analysis applicable in the forensic field. Relevance to the forensic analysis is that besides generation of standard STR‐profiles, DNA repeats can also be sequenced to look for polymorphisms. Furthermore, additional SNPs can be sequenced to acquire information on ancestry, paternity or phenotype. The current MPS systems are also very helpful in cases where only a limited amount of DNA or highly degraded DNA has been secured from a crime scene. If enough autosomal DNA is not present, mitochondrial DNA can be sequenced for maternal lineage analysis. These developments clearly demonstrate that the use of NGS will grow into an indispensable tool for forensic science.
Microfluidic devices may offer various advantages for forensic DNA analysis, such as reduced risk of contamination, shorter analysis time and direct application at the crime scene. Microfluidic chip technology has already proven to be functional and effective within medical applications, such as for point-of-care use. In the forensic field, one may expect microfluidic technology to become particularly relevant for the analysis of biological traces containing human DNA. This would require a number of consecutive steps, including sample work up, DNA amplification and detection, as well as secure storage of the sample. This article provides an extensive overview of microfluidic devices for cell lysis, DNA extraction and purification, DNA amplification and detection and analysis techniques for DNA. Topics to be discussed are polymerase chain reaction (PCR) on-chip, digital PCR (dPCR), isothermal amplification on-chip, chip materials, integrated devices and commercially available techniques. A critical overview of the opportunities and challenges of the use of chips is discussed, and developments made in forensic DNA analysis over the past 10–20 years with microfluidic systems are described. Areas in which further research is needed are indicated in a future outlook.
The extraction and recovery efficiency of swabs used to collect evidence at crime scenes is relatively low (typically <50%) for bacterial spores and body fluids. Cell‐free deoxyribonucleic acid (DNA) is an interesting alternative compared to whole cells as a source for forensic analysis, but extraction and recovery from swabs has not been tested before using pure DNA. In this study cotton, foam, nylon flocked, polyester and rayon swabs are investigated in order to collect pure DNA isolated from saliva samples. The morphology and absorption capacity of swabs is studied. Extraction and recovery efficiencies are determined and compared to the maximum theoretical efficiency. The results indicate that a substantial part of DNA is not extracted from the swab and some types of swab seem to bind effectively with DNA. The efficiency of the different types of swab never exceeds 50%. The nylon flocked 4N6FLOQSwab used for buccal sampling performs the best.
Microfluidic devices offer important benefits for forensic applications, in particular for fast tests at a crime scene. A large portion of forensic applications require microfluidic chip material to show compatibility with biochemical reactions (such as amplification reactions), and to have high transparency in the visible region and high chemical resistance. Also, preferably, manufacturing should be simple. The characteristic properties of cyclic olefin copolymer (COC) fulfills these requirements and offers new opportunities for the development of new forensic tests. In this work, the versatility of COC as material for lab-on-a-chip (LOC) systems in forensic applications has been explored by realizing two proof-of-principle devices. Chemical resistance and optical transparency were investigated for the development of an on-chip presumptive color test to indicate the presence of an illicit substance through applying absorption spectroscopy. Furthermore, the compatibility of COC with a DNA amplification reaction was verified by performing an on-chip multiple displacement amplification (MDA) reaction.
Accurate DNA quantification is a highly important method within molecular biology. Methods widely used to quantify DNA are UV spectrometry and fluorometry. In this research, seven different DNA samples and one blank (MilliQ ultrapure water) were quantified by three analysts using one spectrophotometric (i.e., a NanoDrop instrument) and three fluorometric (i.e., the AccuGreen High Sensitivity kit, the AccuClear Ultra High Sensitivity kit, and the Qubit dsDNA HS Assay kit) methods. An analysis of variance (ANOVA) scheme was used to determine the influence of the analyst, the method, and the combination of analyst and method, on DNA quantification. For most samples, the measured DNA concentration was close to or slightly above the concentration of 10 ng/L as specified by the supplier. Results obtained by the three analysts were equal. However, it was found that, compared to the fluorometric kits, the used spectrophotometric instrument in the case of fish DNA samples tends to overestimate the DNA concentration. Therefore, if sufficient sample volume is available, a combination of a spectrophotometric and a fluorometric method is recommended for obtaining data on the purity and the dsDNA concentration of a sample.
Already for some decades lateral flow assays (LFAs) are ‘common use’ devices in our daily life. Also, for forensic use LFAs are developed, such as for the analysis of illicit drugs and DNA, but also for the detection of explosives and body fluid identification. Despite their advantages, including ease-of-use, LFAs are not yet frequently applied at a crime scene. This review describes (academic) developments of LFAs for forensic applications, focusing on biological and chemical applications, whereby the main advantages and disadvantages of LFAs for the different forensic applications are summarized. Additionally, a critical review is provided, discussing why LFAs are not frequently applied within the forensic field and highlighting the steps that are needed to bring LFAs to the forensic market.