 E-mail
for more information
Company's
other products
E-mail
to a colleague
See
similar products
Printer
friendly format
|
|
Moving Towards Portable: Electrophoretic techniques in forensics and disaster genetics
Dr. Stuart Hassard
Within forensic analysis, there is a growing need to move towards portable detection systems. This need occurs in the civilian fields of crime scene trace analysis and disaster genetics - the identification of remains after a natural disaster or terrorist events. There is a direct parallel between the potential specifications of these civilian forensics systems and those suitable for the detection of bio-threats in the defense arena.
Most detection systems for these analyses involve the use of labels. Such labels may be fluorescent or chemiluminescent and act to amplify the signal to ensure detection of the potential pathogen at low concentration. The use of labels may require cold-chain logistics and biochemistry facilities, and each potential threat may require its own labeling or identification system. As such, most current detection systems cannot be integrated with each other, and the perfect solution of a universal detection system for most if not all threats is not possible using current labeled technology where different analyses require different optical apparatus, labels, and detector systems.
Forensics
Forensic analysis is an expansive discipline needing accurate and verifiable collection and analysis of a wide range of samples, such as faeces, urine, blood, and semen. Analyses within this range of possible samples include nucleic acids (DNA and RNA), proteins (i.e., lifestyle markers such as carbohydrate-reduced transferrin for alcoholism) and small molecules (i.e., alkaloids, cannabinoids, and explosive breakdown products). This calls for a large selection of detection modalities, often with dedicated analysis equipment. The ideal situation will be the development of integrated or single systems capable of multi-entity detection and analysis, allowing genomic, proteomic, and chemical analysis in the field.
Disaster genetics
The identification of individuals post-disaster, whether by terrorist atrocity, war crime, or natural disasters, needs to be fast, simple, and accurate, and preferably done onsite. By far, the most precise way of achieving this, where physical or dental records are inappropriate due to location or sample degradation, is DNA analysis. For instance, the use of single nucleotide polymorphisms (SNPs) to identify victims of 9/11, as well as mitochondrial DNA analysis of tsunami victims, have now been established as routine laboratory techniques.1,2 What this area is missing, however, are field-deployable systems to enable at-site rapid analyses, allowing for the rapid identification and, for example, regrouping of body parts or family members, thus eliminating the need for undignified and distressing storage in makeshift facilities.
Current analysis systems are lacking
The most mobile systems that this author has seen are based on 4-ton trucks with a "clean" lab, consisting of standard lab equipment such as centrifuges, PCR machines, and gel electrophoresis equipment. The need for smaller, self-contained systems, preferably portable and capable of fairly complex analyses, is paramount.
Forensics and disaster genetics are still largely lab-based disciplines. Trace samples have to be collected using swabs or other collection systems and transported to the site of analysis, causing delays and possible contamination issues. A number of key technologies underline these analytical procedures - most of which are based on the separation and sizing of molecules. In the case of DNA samples, this is often following polymerase chain reaction (PCR) amplification. These techniques (1-D polyacrylamide gel electrophoresis [PAGE], 2D-PAGE, and so on) are well established and remain workhorse technologies today despite, in the case of PAGE, poor detection limits, restricted resolution, and quantification and complex operation that does not lend itself to non-technical users or field deployment.
High-quality data also can be obtained using mass spectroscopy, and it provides excellent sensitivity and precision, but at considerable expense in terms of both instrument cost and skilled users. Even at the less expensive end of the market, capital costs are high, and as a result, MS technology is generally available only in core facilities, which can entail substantial waiting time and reduction in analysis efficiency.
Label-free systems and microfluidics
Universal detection is possible using systems where the detection is label-independent, such as mass spectroscopy. First-generation capillary electrophoresis (CE) systems were capable of some form of label-free detection, but were large and unfeasible as potential field-deployable systems. Second-generation systems have been developed employing robust engineering and improved signal processing that make their improved data quality and ruggedness applicable in the field.
Figure 1: An 8-channel label-free intrinsic imaging (LFII) SU8 positive mold |
Furthermore, a major part of the development of such systems will also entail the removal of the capillary component and the addition of microfluidic chips as the separation environment.3
Microfluidic systems have the following manifest advantages and will be enabled by the application of new label-free technologies:
• Chips are easily replaced in the system and cheap enough to be one-use disposable, allowing no chance of cross-contamination.
• Direct real-time visualization of molecule separation is possible, and entities and reaction components can be manipulated in real time, allowing the potential for lab-on-a-chip analysis. This is enabled because proteins can maintain their functionality, as they can be separated and/or manipulated without attached labels.
• Analyzed unlabeled molecules can be switched to other systems such as mass spectroscopy.
• Miniaturization…. Separations on microfluidic chips are routinely achievable in mm topologies,
allowing separations comparable to capillaries. The topologies, with channels looping back and forth, also allow long separations to be achieved, with over a meter of channel possible on a standard 10-cm silicon wafer. Multiple channels can also be fabricated on the same chip and used sequentially or simultaneously. Figure 1 shows an 8-channel LFII chip mold with the channels traversing a common detector window. The channel length is 23 cm and the channel dimension 100 mm deep by 50 mm wide.
Basic specifications of a field-portable device
In many ways, the needs of civilian forensics devices and military/defense detection-based systems are in total alignment; therefore, a set of basic military system specifications can be used to define the system.
Key elements of military requirements include:
• Full automation
The system should be designed to be stand-alone; ideally, each of the components will form a module that can be separately removed and replaced. The whole unit will be aimed at providing the simplest graphic user interface (GUI) possible. Chemicals, separation systems, and primers will be deliverable by cassettes, hopefully without resorting to a cold chain. The data delivery will be wireless, with built-in, self-diagnostic systems.
• Fewer logistics support requirements (i.e., fewer consumables, less-sensitive reagents)
Chemicals such as fluorescent markers currently used in lab-based analysis introduce an extra level of complexity, with light sensitivity or a short life span. Storage of such materials in a remote unit is sub-optimal. Inci-
dentally, no labels also means that no cold chain is necessary.
• The ability to identify all threats
Chemical, biological, as well as pathogenic organisms will be detected.
• Rapid response
The potential for rapid diagnosis improves in microfluidic systems, and separations occur in a very small
distance.
• Continuous operation, robustness, and reliability
The system will be optimized for ease of use in difficult situations by non-scientific operatives.
The need for informatics
The last requirement for this putative device is informatics. In addition to the software that runs the system, it is paramount that the end product is presented and disseminated in a way that enables decision-making and response in a timely fashion. Such distributed data acquisition models have formed part of the UK e-Science program (www.www.nesc.ac.uk). This well-funded program was designed to build data acquisition and handling systems for many applications
over the next five to 15 years (www.nesc.ac.uk/nesc/define.html). A typical example of an e-science consortium is DiscoveryNET (www.discoveryonthe.net), a project that is developing middleware technology that allows users to create knowledge discovery applications over grid-based resources. The aim of DiscoveryNET is to build a collaborative environment for the development of scientific applications that integrate the analysis of data generated from high-throughput experiments with the wealth of available online data resources using distributed computing resources.
Summary
The concepts outlined in this article predict the evolution of forensics from an interior science to an exterior one. This it not an 'if' scenario, and as the world changes and faces new challenges, the technologies to protect our society will have to evolve as well. If the change in personal computing over the last 10 years is used as a model, the change in biotechnology and the impact on forensics over the next 10 years will be amazing. One thing is certain, field-based systems have to be developed, and they will be label-free.
References
1. http://www.prnewswire.com/cgi-bin/stories.pl?ACCT=104&STORY=/www/story/08-29-2002/0001791284&EDATE
2. http://www.genecodesforensics.com/about
3. http://www.rsc.org/publishing/journals/LC/article.asp?type=CurrentIssue
Dr. Stuart Hassard is the
Co-founder and Head Biologist
at DeltaDOT Ltd. He may be contacted
at ChromatographyTechniques@advantagemedia.com.
DeltaDOT Ltd.
Bessemer Building (RSM), Prince Consort Road
London
|
