Enzyme discovery may benefit Homeland Security and Industry

Research & Development Update

Novel sensor and decontamination systems for homeland security, environmental protection and energy generation, as well as new industrial chemials and separations, may be possible thanks to research being done at the U.S. Dept. of Energy's Pacific Northwest National Laboratory (PNNL; Richland, WA). Scientists there have successfully immobilized enzymes while simultaneously enhancing their activity and stability.

Previous attempts to immobilize soluble enzymes with various solid materials have been disappointing because only small amounts of the immobilized enzymes showed any biological activity, says molecular biologist Erik Ackerman. "For the first time, we have immobilized an enzyme at high concentrations in a way that actually enhances its stability and activity." In lab tests, they nearly doubled the activity levels of organophosphorus hydrolase, an enzyme known for its potential for biosensing and decontaminating poisonous agents.

To achieve enhanced stability and activity, Ackerman and his colleagues modified existing nanoporous silica originally developed at PNNL to sequester mercury for environmental remediation. The material, called SAMMS - for self-assembled monolayers on mesoporous supports - contains uniform pores, the size of which can be tailored to suit the application. In this case, the pores were enlarged to 30 nm, which is large enough to accommodate the immobilized enzyme. Then, the pore surfaces were coated with a specific chemical compound to provide an optimal environment for enzyme activity and stability, he explains.

Gold Nanoparticles:

Harvesting them from Alfalfa Plants...

Plants use their roots to extract nutrients - water, minerals, even heavy metals - from the soil. So a team of researchers from the Univ. of Texas's El Paso and Austin campuses is investigating whether alfalfa can extract gold from various growth media. If it works, using plants to produce gold nanoparticles would eliminate the need for harsh chemicals or chemical reducing agents, says Jorge Gardea-Torresdey, professor of chemical and environmental sciences.

Alfalfa plants were germinated and grown on an artificial, gold-rich soil-like medium. Analysis of samples confirmed the existence of gold nanoparticles in the roots and along the entire shoot of the alfalfa plants, and determined that the particles have physical properties (e.g., oxidation resistance, and thermal and electrical conductivity) similar to gold nanoparticles formed using chemical techniques. The next question the researchers aim to answer is how to extract the nanoparticles from the alfalfa, which may be by centrifuge, they say.

... and Using them to Detect Biological Agents

A new method for detecting infectiousdisease agents, including those associated with many bioterrorism and warfare threats, has been developed by scientists at Northwestern Univ. (Evanston, IL).

The new detection technique involves designing DNA detection probes for each disease agent. Each probe consists of a tiny gold particle approximately 13 nm in diameter. Attached to the particles are two key items: molecules that provide a unique signal when a light is shined on them (like a fingerprint), and a single strand of DNA designed to recognize and bind to a target of interest, such as anthrax, smallpox or hepatitis A.

These probes are used with a chip spotted with strands of DNA designed to recognize different disease targets. If a disease target is present in the sample being tested, it binds to the appropriate spot on the chip. Corresponding nanoparticle probes latch onto any matches. The chip is then washed and treated with photographic developing solution, and silver coats the gold nanoparticles where a match has taken place. A laser is scanned across the chip, and the signals for the probes are recorded.

The silver enhances the signal by many orders of magnitude, creating a highly sensitive method for detecting DNA, explains Chad A. Mirkin, director of Northwestern's Institute for Nanotechnology. "Our technique seems to surpass conventional fluorescence-based methods in almost every category - sensitivity, selectivity, ease of use and speed - and has the potential to be inexpensive," he adds.

Compounds May Immobilize AIDS Virus and Radioactive Waste

A series of compounds - niobium heteropolyanions (HPAs) - that could potentially immobilize the AIDS virus or selectively extract radionuclides from nuclear waste sites has been discovered by May Nyman, a researcher at Sandia National Laboratories (Albuquerque, NM). Nyman found the right conditions to synthesize the first niobium HPA, and then tweaked the process to create an assortment of compounds.

She reports that these are the first niobium HPAs, although HPAs in the form of oxides of vanadium, tungsten and molybdenum have been known since the late 19th century. Unlike other HPAs, though, niobium HPAs are basic (rather than acidic), which means they can survive longer, and possibly even thrive, in the basic or neutral environments of radioactive wastes and blood, respectively.

Preliminary work at the Savannah River Site indicates that the new compounds do indeed selectively remove certain radionuclides from waste solutions. To evaluate the compounds' virus-binding ability, researchers have tested various HPA compositions, and have found that HPAs with small amounts of iron or niobium have an especially strong binding effect. "Now we have HPAs that are completely niobium," Nyman points out.

"Smart Dust" Particles May Detect Biological and Chemical Agents

Researchers at the Univ. of California, San Diego have developed dust-sized chips of silicon that can quickly and remotely detect biological and chemical agents, including substances that a terrorist might dissolve in drinking water or spray into the atmosphere, says Michael J. Sailor, professor of chemistry and biochemistry who headed the project.

Silicon wafers are encoded by generating layers of nanometer-thick porous films on the wafers using a special electrochemical etch. This layered structure on the dust-sized particles, which are created by breaking apart the wafer using ultrasound, imparts unusual optical properties to the particles. These micron-sized particles, referred to as photonic crystals, reflect light of very precise colors, each one of which can be thought of as a single bar of a bar code.

"A particle that is as small as a piece of dust and that has some intelligence built into it could be inconspicuously stuck to paint on a wall or to the side of a truck, or dispersed into a cloud of gas, to detect toxic chemicals or biological materials," explains Sailor. "When the dust recognizes what kinds of chemicals or biological agents are present, that information can be read like a series of bar codes by a laser that's similar to a grocery store scanner to tell us if the cloud that's coming toward us is filled with anthrax bacteria or if the tank of drinking water into which we've sprinkled the smart dust is toxic."

Recycling Waste Chips Could Expand the Uses for Nanocrystals

Engineers at Purdue Univ. (West Lafayette, IN) have made a surprising discovery that could open the door to new applications for metal nanocrystals, which are often harder, stronger and more wear-resistant than the same materials in bulk form. Nanocrystals have been too expensive and difficult to produce to be of any practical commercial use, with a cost of at least $100/lb, notes Srinivasn Chandrasekar, professor of industrial engineering. Furthermore, nanocrystals of certain metals cannot be made at all with present laboratory techniques, he adds.

Chandrasekar and Dale Compton, also a professor of industrial engineering, have discovered that the chips left over from machining operations are either entirely or primarily made of nanocrystals. The chips, which are shaved away from metals as they are machined, are ordinarily collected as scrap, melted down and reused. But melting the chips turns the nanocrystals back into ordinary bulk metals, removing their high strength, wear resistance and other unusual properties.

So Chandraseka and Compton looked into saving the chips and processing them for use in other products. They have developed a technique that they believe can be used to make these materials in large quantities at very low cost - no more than $1/lb plus the initial cost of the bulk material. The process involves milling the chips to make powders and then compressing and heating the powders to make metal parts. Nanocrystals produced in laboratories have been subjected to such processs, and they have retained their nanocrystalline properties, the engineers say. However, further research is needed to determine whether the nanocrystals contained in scrap chips retain their properties after processing.

Universities Will Help NASA Develop Space-Age Materials

A consortium of research institutions, with funding from the National Air and Space Administration (NASA), will establish the Institute for Biologically Inspired Materials (IBIM). The institute's mission is to boost understanding of natural phenomena and translate its findings into new materials that mimic the extraordinary structural and self-repairing properties of such substances as bone or seahells, says Edward Samulski, professor of chemistry at the Univ. of North Carolina and the leader of UNC's part in the effort. The other participants are the Univ. of California at Santa Barbara, Princeton Univ., and Northwestern Univ., as well as the Institute for Computer Applications in Science and Engineering (ICASE) at the NASA Langley Research Center.

"It's a rather ambitious thing to design materials that can not only recognize when they've been damaged but can indicate the exact site and take steps to repair it," says Samulski. "In a sense, it's at the fringes of science fiction. These so-called `self-healing' materials could be critical to space exploration, because a meteor particle even as small as a grain of sand could puncture the hull of existing space vehicles."

"Our goal is to bring more 'smart' functions into spacecraft materials," explains Ilhan Aksay, professor of chemical engineering at Princeton who leads the institute. "Some of these functions already exist in biology."