Small groups or individuals can use advanced technology to cause massive destruction, and the rapid pace of technology and ease of information dissemination continually gives terrorists new tools. A 100% defense is not possible. It's a numbers problem – there are simply too many possible targets to protect and too many potential attack scenarios and adversaries to defend against.

However, science and technology (S&T) is a powerful force multiplier for defense. We must use S&T to get ahead of the game by making terrorist attacks more difficult to execute, more likely to be interdicted, and less devastating in terms of casualties, economic damage, or lasting disruption. Several S&T areas have the potential to enhance homeland security efforts with regard to detecting radiation, pathogens, explosives, and chemical signatures of weapons activities. All of these areas require interdisciplinary research and development (R&D), and many critically depend on advances in materials science.

For example, the science of nuclear signatures lies at the core of efforts to develop enhanced radiation detection and nuclear attribution capabilities. Current radiation detectors require cryogenic cooling and are too bulky and expensive. Novel signatures of nuclear decay, new detector materials that provide high resolution at ambient temperatures, and new imaging detectors are needed. Such technologies will improve our ability to detect and locate small, distant, or moving sources and to discriminate between threat materials and legitimate sources. A more complete understanding of isotopic ratios via secondary ion mass spectrometry (SIMS), NanoSIMS, or yet-to-be-developed technologies is required to elucidate the critical characteristics of nuclear materials to identify their source and route history.

S&T challenges abound in the biodefense arena. Improved biodetectors are needed – autonomous instruments that continuously monitor the environment for threat pathogens, promptly alert authorities in the event of a positive detection, and have an extremely low false alarm rate. Because many threat pathogens are endemic to various regions of the world, the natural microbial environment must be characterized so that background detections can be distinguished from a deliberate release. In addition, most current detection approaches require an a priori knowledge of the pathogens of concern, which won't work in the face of a new, naturally occurring disease, such as a mutated avian influenza that affects humans, or a deliberately manipulated organism. Thus, we must move from species-specific detection to function-specific detection based on a fundamental understanding of the mechanisms and genetic markers of infectivity, pathogenicity, antibiotic resistance, and other traits that distinguish a harmful organism from an innocuous one. Last but not least, new vaccines and treatments are needed, which in turn require in-depth understanding of cellular surfaces, protein folding, and myriad nano-bio aspects of host-pathogen interactions.

Much attention is being devoted to countering weapons-of-mass-destruction terrorism, since al-Qaeda and other terrorist groups have repeatedly stated their intention to acquire and use nuclear, chemical, or biological weapons. However, terrorists continue to wreak havoc using improvised explosive devices. Thus there is a pressing security need for better methods of detecting explosive materials and devices. Pulsed fast-neutron analysis or terahertz spectroscopy for material- and element-specific imaging offer the promise of greatly improved explosive detection. For bio-based approaches, the development of highly multiplexed transducer arrays and molecular recognition methods that mimic biological systems would similarly provide the foundation for vastly improved capabilities.

Likewise, new materials and technologies are needed for the detection of chemical signatures of weapons activities. One grand challenge is the detection and characterization of chemical effluents indicative of weapons production, either biological, chemical, or nuclear. Ideally, one would like to be able to do this remotely. One must know what chemicals, singly or in combination, would result in various production processes, how they would behave in the environment, and how those chemicals, their precursors, and degradation products could be sampled. One must then devise an appropriate detection technology, together with the necessary pointing and tracking, data analysis, and communications systems. All of this must fit on an airborne platform or satellite and be able to function reliably in a hostile, high-altitude environment.

Clearly, these are no small feats. Multidisciplinary collaborations among national labs, universities, and industry will be needed to tap the full range of innovation embodied by the broad science and engineering community. Partnerships with user communities, such as first responders and port and border security officials, are also essential. The results must not only meet user needs and be affordable, they must be compatible with a wide range of customer operating and training systems. I am confident that homeland security S&T challenges can be met. New homeland security capabilities will not only protect against terrorist attack, they will bring great benefits to public health, environmental monitoring, and many other spin-off applications.

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DOI: 10.1016/S1369-7021(06)71553-X