Protection and Decontamination of Surfaces
By L.C. Feldman
Innovative surface science plays a cross-cutting role in sensing, protection and decontamination. While there is a need to detect and identify agents that could be delivered in an attack, it is also necessary to develop systems that are constantly protecting personnel and buildings against foreign agents, hopefully destroying them on contact. In general there is a lack of materials and methods for the large-scale remediation of bioterrorism pathogens or for the clean-up of disinfecting agents.
Decontamination methods most likely to be successful are different from those normally used in a military incident, which are corrosive and/or toxic and can cause collateral damage to people, facilities and equipment. The optimum technology—and hence the challenge—will be non-toxic, non-corrosive and easily deployable. Methods should allow for detoxification and degradation to environmentally acceptable components, rather than complete destruction. Effective decontamination also requires effective sampling/sensing and verification methods to ensure the "clean-up" goal. Finally, the methods must be defensible to regulatory agencies and the public.
There is a special interest in the development of passive, self-cleaning or continuously acting methods for preventing the contamination of exposed air, water, food, uniforms, or surfaces. A particular scientific direction under study is in the area of photocatalytic inactivation. This relatively new technology has the advantage of being passive, and also acts at room temperatures, and has the ability to destroy pathogens without affecting personnel. When a specific photocatalyst, such as titanium dioxide (TiO2), is illuminated with near ultraviolet light of wavelengths less than 385 nm, photons are absorbed and electron holes are produced in the material. The holes are very oxidizing and can be used to destroy organisms. Such photocatalysts have been used for disinfection. There is still a need to determine the mechanism of destruction, particularly in the case of spore-forming organisms, as well as a need to study the use of these UV photocatalytic processes under a variety of humidity scenarios. "On board" UV sources also become another important research endeavor.
Other methods of disinfection such as microwave radiation, high-intensity pulsed UV light, and electron beams, would likely only be used in places where personnel are absent. These have specific applications and can be used under given sets of conditions. For example, it might be possible to use ionizing radiation under proper containment for the decontamination of envelopes and other postal packages. These are also systems that should be considered for given scenarios and research is needed in smaller devices to accomplish the delivery of these types of irradiation.
There is need for the development of methods, devices, and equipment for the decontamination of both indoor and external environments. New equipment and methods of delivery are required, and need to be developed and tested, for the decontamination of large-scale areas composed of complex surfaces and sensitive substrates. In this regard, the delivery of disinfecting agents with nanoparticle carriers is of interest, although there is a cautionary note about the respiratory aspect of this process. Methods are needed to remove the disinfecting agents after their jobs have been accomplished. There is interest in refining existing and new methods in order to fully optimize their safety and benefits. Special interest exists in the development of means for decontamination that carry a unique signature, which can be used to assist in the identification of the levels and location of efficacious action, or which can be conveniently monitored to verify clean up or absence of residuals.
Other scientific areas which are relevant to the subject include the following:
- Microfluidics for very local delivery of decontaminants;
- Microstructured materials, such as self-modifying sensory polymers;
- Organic/inorganic materials integration;
- New materials and processes for mitigation of chemical-bio threats, such as the development of microfibrous carrier materials and enhanced electrostatic filtration and self-cleaning techniques;
- Nanostructured fabrics, such as self-detoxifying clothing liners for chemical and biological protective clothing;
- Nanomolecular therapeutics for force protection, such as the development of non-toxic oil-in-water emulsions that can kill a broad range of spores, bacteria, yeast, and enveloped viruses but are safe for contact with humans, environment and sensitive equipment; and
- Nanoporous materials and strategies for selective filtration and detection of nerve gases, such as semiconducting metal oxides like WO3 and SnO2 that display size selectivity in their reactivity with various bio-toxic reagents.