Washington, January 30 : A scientist duo at the Georgia Tech Research Institute (GTRI) has developed prototypes of a rapid, non-disruptive and less expensive method that may be used to decontaminate bioterrorism hazards in future.
Brent Wagner and Hisham Menkara, who worked in collaboration with Austin-based Stellar Micro Devices, Inc. (SMD), say that anthrax spores can be killed in two to three hours without any lingering effects by using flat panel modules that produce X-rays and ultraviolet-C (UV-C) light simultaneously.
The system is also capable of killing anthrax spores hidden in places like computer keyboards without causing damage, say the researchers.
"This is certainly an improvement over previous techniques. The UV-C attacks spores on surfaces and the X-rays penetrate through materials and kill spores in cracks and crevices," said Brent Wagner, GTRI principal research scientist and director of its Phosphor Technology Center of Excellence (PTCOE).
The researchers say that both types of radiation can penetrate the outer structure of an anthrax spore to destroy the bacteria inside, compared to the current decontamination standard-chlorine dioxide gas-that kills microorganisms by disrupting transport of nutrients across the cell wall, but cannot reach hidden spores.
With current decontamination standard, hard surfaces must be cleaned independently with harsh liquid chlorine dioxide, and people cannot re-enter a room fumigated with chlorine dioxide until the gas is neutralized with sodium bisulfite vapour and vented from the building.
The new decontamination system resembles a coat rack with radiation modules arranged on rings at various heights that face outward to broadcast radiation throughout a room. As the X-rays and UV-C are lethal at the flux densities used, the system operates unattended and is turned on outside the affected space.
UV-C light in the modules is produced using the optical and electrical phenomenon of cathodoluminescence. Arrays of cold cathodes, each acting like the electron gun in a cathode ray tube, are used to generate numerous electron beams.
"When an electron beam hits a powder phosphor, it luminesces and emits visible and/or non-visible light," explained Hisham Menkara, a senior research scientist in GTRI's Electro-Optical Systems Laboratory.
After investigating many different phosphors, the researchers came to the conclusion that lanthanum phosphate:praseodymium (LAP:Pr) was the most efficient phosphor, with a power efficiency near 10 percent.
While working in the lab, Menkara created the phosphor by mixing precursors lanthanum oxide, hydrogen phosphate and praseodymium fluoride in a glass beaker with methanol (CH3OH) and ammonium chloride (NH4Cl). Air drying the mixture in a fume hood caused the methanol to completely evaporate.
The researchers crushed the resultant cake into a fine powder, heated it in a furnace to a temperature as high as 1250 degrees Celsius for two hours, and crushed it again.
They found that adding lithium fluoride (LiF) and reducing the praseodymium concentration increased the cathodoluminescent properties of the LAP:Pr phosphor.
With the improved phosphor, lab tests conducted by SMD showed that the combined X-ray and UV-C decontamination system could kill anthrax spores.
The research team hopes to develop new UV-C phosphors that can achieve cathodoluminescent efficiency higher than 10 percent, with an emission spectrum that provides increased coverage of the DNA absorption curve.
They say that increased efficiency may make UV-C panels viable for sterilizing medical equipment or purification applications.
"We may be able to use UV-C panels to clean wastewater, which would be better than the lamps currently used. In the environment where the lamps must operate, they are very difficult to clean, whereas flat panels could be cleaned with a squeegee," said Eaton.
The new approach may also be used to kill viruses in buildings used to house chickens. Currently, one has to remove the chickens and raise the temperature in the chicken houses for several days to deactivate the virus.
"With the combined UV-C/X-ray system, you could turn the system on for a few hours, kill the viruses and as soon as you turn it off, the chickens could come right back in," said Wagner.