Every Cell Has A Story To Tell

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Crime scene investigation requires collection and analysis of biological evidence for DNA genotyping. Blood, sperm, and epithelial evidence left behind by perpetrators can help investigators acquire a genetic profile of the person who committed the crime.

A problem occurs when a single evidence sample consists of biological fluids contributed by two or more persons (e.g. the victim and the perpetrator). Commonly, forensic scientists refer to these samples as “mixed biological evidence.”

Current approaches to mixed biological evidence analysis have limitations, due to the fact they produce mixed genetic profiles, which can only be interpreted by statistical assumptions that introduce uncertainty and often compromise the forensic value of laboratory findings.

The DEPArray NxT™ is a new benchtop instrument that resolves this uncertainty by enabling forensic laboratory scientists to separate blood cells, from epithelial cells, from sperm cells, with 100% precision. Such separation, prior to genetic analysis, allows distinct profiling of multiple individual contributors by routine DNA identification methods.

The workflow below allows the recovery of multiple groups of 100% pure samples for clear-cut genetic profiling.

Cells selected, isolated, and collected by the DEPArray system are compatible with DNA-based human identification kits, instrumentation, and software from a variety of suppliers.

The DEPArray NxT™ system is non-destructive, and is even used to prepare pure populations of living cells for non-forensic genetic research applications. Cells selected, isolated, and collected by the DEPArray NxT system are compatible with DNA-based human identification kits, instrumentation, and software from a variety of suppliers.

With the ability to analyze even minute mixed biological evidence, the DEPArray NxT™ system can separate epithelial cells, white blood cells, and sperm cells, and recover 100% pure pools of cells for standard forensic analysis. Profiles produced from these separated samples represent a fundamental step in assigning the precise and distinct genetic fingerprints from each contributor.

When a sample is composed of a single cell type (such as epithelial cells, or sperm cells), but the contribution of multiple individuals is suspected, the ability of the DEPArray NxT™ system to single out and collect single cells for analysis enables confident DNA-based identification, based on unambiguous STR profiles, of more than one individual.

The newly developed DEPArray™ Forensic Sample Prep Kit streamlines the sample preparation step before DEPArray NxT sorting with a labor-saving and standardized procedure. The kit includes all the reagents to process the sample from the evidence support material to the DEPArray NxT cartridge and has been specifically designed for the staining of epithelial, sperm and white blood cells before DEPArray NxT sorting.

Now the genetic characterization of minute biological evidence can be achieved with the latest genotyping technologies. The ultimate challenge is to retrieve crucial information from mixed evidence as DNA analysis will produce a mixed genetic profile. DEPArray™ NxT resolves heterogeneity in complex biological mixtures by separating pure cell populations, even from minute biological evidence. Downstream analysis of pure cells isolated with DEPArray NxT with standard forensic methods produces clear-cut genetic profiles of each contributor.

The DEPArray NxT™ system is designed with a friendly user interface and allows one to rapidly obtain 100% pure cells with reduced operator interaction. The next-generation software permits quicker selection of cells of interest with an exceptional level of accuracy, reproducibility, and high-quality images.

The DEPArray™ NxT system consists principally of a fluorescence microscope, a digital camera, software, and a disposable microfluidic cartridge managing a thin liquid volume. The system examines mixed cell suspensions for cell characteristics such as size, morphology, surface markers, and DNA content. Dielectrophoretic forces induced under software control enable single cell entrapment and mobilization, for selection, isolation, and recovery of specific, individual cells. The system is differentiated from conventional cell sorting and selection technologies by the ability to pick out specific, individual cells, from a complex heterogeneous sample, for isolation, collection, and analysis.

The DEPArray NxT™ system’s CellBrowser™ software enables image-based selection and recovery of specific cells and cell populations in a sample. The fluorescence and bright field selection criteria are user-defined, allowing maximum flexibility for isolation of any rare cell type for which fluorescence markers are available.

Key features of CellBrowser™ software includes:

  • Automatic collection of values such as peak and mean intensity, roundness, and diameter for each fluorescence channel
  • Multiple, user-defined filtering criteria to classify and select target cells
  • Various display options including scatter plots, histograms, and tables
  • Easily adjusted gating thresholds

Images of individual events can be viewed on an image bar, allowing cells of interest to be identified and flagged for recovery. Cell perimeter, diameter, and circularity can also be viewed in the bright field channel and allow isolation of morphologically distinct subsets of cells, while ensuring recovery of only intact, individual cells exhibiting the desired fluorescence patterns.

The unique benefits of DEPArray NxT™ include:

  • Resolves heterogeneity in complex biological mixtures by separating pure cell populations from even minute biological evidence.
  • New CellBrowser™ software for image acquisition, enables real-time visualization and interaction with all cell populations. The option to preset target-selection criteria reduces the hands-on time of the operator.
  • External barcode reader for sample-positive identification and unambiguous operator identification.
  • Lighter and more compact design, in fact the DEPArray NxT allows a wider operational area for the user.
  • The option to enable the simultaneous recovery of samples using a 96-well plate.

For more information, visit the Menarini Silicon Biosystems website.

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Digital-Image Management at Mass Gravesites

SKELETONIZED REMAINS that were carefully unearthed from the desert sands of Iraq tell their own story: the bones of an adult, still dressed in a woman’s apparel, lie supine. The skull is perforated by a bullet hole. Tucked in the space between the ribs and the left humerus is a much smaller skeleton, bones in the skull un-fused, and the fully clothed body partially swaddled in a blanket.