Forensic Science

A Lateral Flow Biosensor Based on Isothermal Amplification for Visual Identification of Species and Sex from Bloodstain

The prompt species identification from biological samples at a crime scene can rapidly filter out truly valuable biometric information for subsequent personal identification. Meanwhile, early sex determination can assist in narrowing the pool of suspects. However, the current methods for forensic DNA analysis, particularly in point-of-care scenarios, are often limited by the intricate equipment for signal generation and the laborious procedure for DNA purification. The present study introduces a novel portable lateral flow biosensor that possesses extraction-free and anti-aerosol characteristics for on-site determination of species and sex. The bloodstain can be directly submitted to loop-mediated isothermal amplification (LAMP) for the analysis of both mitochondrial and nuclear DNA. The incorporation of a lateral flow device with gold magnetic nanoparticle probes allows for visual interpretation of results through colorimetric signals while also preventing interference on result judgment from pigments such as hemoglobin. Carryover contamination, which is a disharmonious factor in LAMP, especially as the inherent contradiction derived from uncapping in the lateral flow strategy, has been effectively addressed through the integration of uracil DNA glycosylase without compromising the isothermy throughout the process. As a proof-of-concept experiment, species and sex can be accurately identified within 40 min from trace bloodstains amidst significant background interference by targeting cytochrome b and Y-chromosomal amelogenin. Furthermore, the single-blind study revealed a concordance rate of up to 100% in both simulative degraded and true dated bloodstains. This suggests that this biosensor has the potential to be utilized in forensic DNA analysis at crime scenes.

First experiences with the Spectrum Compact CE System

The newly released Spectrum Compact CE System by Promega is a capillary electrophoresis instrument developed for DNA-fragment separation and sequencing. In this study, its compatibility to 8 commercial short tandem repeat (STR) kits from 4 different manufacturers, reproducibility (sizing precision, accuracy and concordance) and robustness (sensitivity and mixture resolution) were tested and compared to the ABI PRISM® 310 Genetic Analyzer. The instrument was able to successfully analyse amplicons of all tested kits, proved to be as precise as claimed by manufacturer specifications and was shown to be more robust than the ABI PRISM® 310 Genetic Analyzer in some aspects. Analyses on the Spectrum Compact CE System were able to resolve peaks with length differences of 1-basepair in the short and long fragment range and mixtures of mixture ratios down to 1:30. We describe the advantages and limitations we have observed so far working with this instrument in our forensic genetics laboratory.

U.S. initiatives to strengthen forensic science & international standards in forensic DNA

A number of initiatives are underway in the United States in response to the 2009 critique of forensic science by a National Academy of Sciences committee. This article provides a broad review of activities including efforts of the White House National Science and Technology Council Subcommittee on Forensic Science and a partnership between the Department of Justice (DOJ) and the National Institute of Standards and Technology (NIST) to create the National Commission on Forensic Science and the Organization of Scientific Area Committees. These initiatives are seeking to improve policies and practices of forensic science. Efforts to fund research activities and aid technology transition and training in forensic science are also covered. The second portion of the article reviews standards in place or in development around the world for forensic DNA. Documentary standards are used to help define written procedures to perform testing. Physical standards serve as reference materials for calibration and traceability purposes when testing is performed. Both documentary and physical standards enable reliable data comparison, and standard data formats and common markers or testing regions are crucial for effective data sharing. Core DNA markers provide a common framework and currency for constructing DNA databases with compatible data. Recent developments in expanding core DNA markers in Europe and the United States are discussed.

Construction of a library of cloned short tandem repeat (STR) alleles as universal templates for allelic ladder preparation

Short tandem repeat (STR) genotyping methods are widely used for human identity testing applications, including forensic DNA analysis. Samples of DNA containing the length-variant STR alleles are typically separated and genotyped by comparison to an allelic ladder. Here, we describe a newly devised library of cloned STR alleles. The library covers alleles X and Y for the sex-determining locus Amelogenin and 259 other alleles for 22 autosomal STR loci (TPOX, D3S1358, FGA, D5S818, CSF1PO, D7S820, D8S1179, TH01, vWA, D13S317, D16S539, D18S51, D21S11, D2S1338, D6S1043, D12S391, Penta E, D19S433, D11S4463, D17S974, D3S4529 and D12ATA63). New primers were designed for all these loci to construct recombinant plasmids so that the library retains core repeat elements of STR as well as 5'- and 3'-flanking sequences of ∼500 base pairs. Since amplicons of commercial STR genotyping kits and systems developed in laboratories are usually distributed from 50 to <500 base pairs, this library could provide universal templates for allelic ladder preparation. We prepared three different sets of allelic ladders for this locus TH01 and an updated version of an allelic ladder for the DNATyper(®)19 multiplex system using these plasmids to confirm the suitability of the library as a good source for allelic ladder preparation. Importantly, the authenticity of each construct was confirmed by bidirectional nucleotide sequencing and we report the repeat structures of the 259 STR alleles. The sequencing results showed all repeat structures we obtained for TPOX, CSF1PO, D7S820, TH01, D16S539, D18S51 and Penta E were the same as reported. However, we identified 102 unreported repeat structures from the other 15 STR loci, supplementing our current knowledge of repeat structures and leading to further understanding of these widely used loci.

Metal-Enhanced Fluorescence and FRET in Multilayer Core-Shell Nanoparticles

In recent years, various methods for the synthesis of fluorescent core-shell nanostructures were developed, optimized, and studied thoroughly in our research group. Metallic cores exhibiting plasmonic properties in the UV and visible regions of the electromagnetic spectrum were used to increase substantially the brightness and stability of organic fluorophores encapsulated in silica shells. Furthermore, the efficiency and range of Förster resonant energy transfer (FRET) between donor and acceptor molecules located in the vicinity of the metallic core was shown to be enhanced. Such multilayer nanoparticle architectures offer, in addition to the aforementioned advantages, excellent chemical and physical stability, solubility in aqueous media, low toxicity, and high detectability. In view of these enviable characteristics, a plethora of applications have been envisioned in biology, analytical chemistry, and medical diagnostics. In this paper, advances in the development of multilayer core-shell luminescent nanoparticle structures and selected applications to bioanalytical chemistry will be described.

Chemical analysis of molecular species through turbid medium

Subsurface analysis of chemical species is imperative for biomedical diagnostics and imaging, homeland security, and pharmaceutical and other industries; however, the access to the object of interest is often obscured by an optically scattering medium which limits the ability to inspect the chemical composition of the sample. In this report, we employ coherent Raman microspectroscopy in a combination with a hierarchical cluster analysis to mitigate the effect of scattering and demonstrate the identification of multiple chemical species.

Label-free biosensing based on multilayer fluorescent nanocomposites and a cationic polymeric transducer

This study describes the preparation and characterization of a DNA sensing architecture combining the molecular recognition capabilities of a cationic conjugated polymer transducer with highly fluorescent core-shell nanoparticles (NPs). The very structure of the probe-labeled NPs and the polymer-induced formation of NP aggregates maximize the proximity between the polymer donor and acceptor NPs that is required for optimal resonant energy transfer. Each hybridization event is signaled by a potentially large number of excited reporters following the efficient plasmon-enhanced energy transfer between target-activated polymer transducer and fluorophores located in the self-assembled core-shell aggregates, resulting in direct molecular detection of target nucleic acids at femtomolar concentrations.

Blood species identification for forensic purposes using Raman spectroscopy combined with advanced statistical analysis

Forensic analysis has become one of the most growing areas of analytical chemistry in recent years. The ability to determine the species of origin of a body fluid sample is a very important and crucial part of a forensic investigation. We introduce here a new technique which utilizes a modern analytical method based on the combination of Raman spectroscopy and advanced statistics to analyze the composition of blood traces from different species. Near-infrared Raman spectroscopy (NIR) was used to analyze multiple dry samples of human, canine, and feline blood for the ultimate application to forensic species identification. All of the spectra were combined into a single data matrix, and the number of principle components that described the system was determined using multiple statistical methods such as significant factor analysis (SFA), principle component analysis (PCA), and several cross-validation methods. Of the six principle components that were determined to be present, the first three, which contributed over 90% to the spectral data of the system, were used to form a three-dimensional scores plot that clearly showed significant separation between the three groups of species. Ellipsoids representing a 99% confidence interval surrounding each species group showed no overlap. This technique using Raman spectroscopy is nondestructive and quick and can potentially be performed at the scene of a crime.