ASU researchers presentations shed light on multiple advances

Kimberly Ovitt, Director of Communication & Institutional Advancement
(480)727-8688 | kimberly.ovitt@asu.edu

Joe Caspermeyer, Media Relations Manager & Science Editor
(480) 727-0369 | joseph.caspermeyer@asu.edu
August 30, 2005

Four teams of Arizona State University researchers made presentations at the 230th national meeting of the American Chemical Society, Aug. 28 – Sept. 1, in Washington, D.C. The topics of the ASU presentations ranged from single molecule electronic devices to new detection systems to guard against terrorist attacks.

Here are brief summaries of the ASU presentations:

Single molecule transistors
A team of scientists led by ASU biophysicist Stuart Lindsay, director of the Center for Single Molecule Biophysics at the Biodesign Institute at ASU, recently created the first reproducible single molecule negative differential resistor (NDR).

"NDR is the basis for memories, switches and logic elements," said Lindsay. "It has been observed in molecules before but never in controlled conditions, never at low voltages, and not in a predictable way."

Lindsay's team designed a molecule, called a hepta-aniline oligomer, which belongs to a group of molecules that biochemists believe is capable of being molecular switches, but which have failed to exhibit those properties in conductance experiments.

The team solved the problem by developing a technique where the molecule could be tested in an electrolyte solution, a condition that past experiments didn't attempt because of interaction problems between the solution and the electrodes. By using a scanning probe microscope with an insulated probe tip to make and measure single-molecule contacts, with molecules designed to bond at their ends with a surface and the probe tip, Lindsay was able to make a reliable connection with single molecules in order to test their behavior.

Lindsay stresses that the main value of the findings is not in having found a molecule that could be developed into a working electrical switch, but in discovering many new critical design parameters that should make possible successful research in designing molecular devices.

"We have a working rational roadmap now for how to do this, and we're already hard at work applying it to a wide variety of potentially exciting applications," he said.

Microorganism eating contaminants
ASU researcher Bruce Rittmann has found an environmentally friendly way to mitigate the human health threat from perchlorate drinking water contamination. Perchlorate is a component of solid rocket fuel.

Recently, the Environmental Protection Agency has grappled with a goal of lowering the perchlorate risk for the population, but current solutions are difficult or very expensive. Because perchlorate cannot be removed by conventional water treatment processes, Rittmann, director of the Center for Environmental Biotechnology at the Biodesign Institute at ASU, has developed a new technology that uses bacteria to render perchlorate contaminated water harmless.

"We are really just harnessing the natural capabilities of microorganisms," said Rittmann, who is also a civil and environmental engineering professor. "What we consider contaminants, they consider food."

The system, called a membrane biofilm reactor (MBfR), uses hydrogen gas as an electron donor to reduce the perchlorate ions to harmless chloride ions (like those found in everyday table salt) and water.

Rittmann, along with collaborators Jinwook Chung, Reid Bowman (Applied Process Technology), and William Wright (California State University, Fresno), report success using the MBfR to treat four contaminated ground waters, each containing perchlorate and nitrate, but also different combinations of chlorate, arsenate, and dibromochloropropane (DBCP). In each case, the MBfR simultaneously reduced nitrate, perchlorate, chlorate, arsenate, and DBCP in the contaminated ground water. Thus, the hydrogen-based MBfR achieved the goal of reducing perchlorate and several other oxidized contaminants in parallel.

New defense for terrorism
The recent terrorism attacks in London and Egypt have further underscored the urgent need to protect the health and safety of our society. In order to thwart future attacks, Joe Wang, director of the Center for Biosensors and Bioelectronics at the Biodesign Institute at ASU, is developing "lab-on-a-chip" systems to detect explosives and chemical warfare agents.

"The long term goal of our research is the creation of a hand-held, field-deployable microanalyzer that can provide for the early and timely detection of explosives and chemical warfare agents," said Wang, who also is a professor in chemical and materials engineering and in chemistry at ASU.

Wang's group has already developed a prototype device to detect TNT and nerve agents. The self-contained apparatus is based on a capillary-electrophoresis electrochemical detection method.

Wang's technology relies on the ability to detect minute chemical changes in explosives when a voltage is applied onto the sensing electrode. A working electrode produces electrons that are taken up by the explosives, reducing the current over time.

The amount of reduction current signal is proportional to the amount of explosives in the sample and is extremely sensitive, able to measure as little as one part per billion. In addition, the method works without any external pumps or valves and the whole detection process can be completed in less than a minute.

Nanomaterial hazard
Preliminary research by a team of ASU scientists suggests the presence of nanomaterials in drinking water may be dangerous to humans. Two of the researchers -- principal investigator Paul Westerhoff and civil and environmental engineering professor John Crittenden -- caution against drawing conclusions from these preliminary results, but they say initial results indicate that certain nanomaterials in water may be toxic.

In the project, the research team simulated liquid found in intestines and introduced into it a layer of colon cells. Then, the cells were exposed to titanium dioxide (TiO2), a nanomaterial commonly used as white pigment. The researchers discovered that exposure to TiO2 dramatically broke down the cellular layer, indicating that the nanomaterial either killed the cells or weakened the cellular junctions.

The results are significant for two reasons. First, it confirms that the body's epithelial, or surface, cells are the first line of defense against nanomaterials. Second, the breakdown of that cellular layer would allow the nanomaterials to get past the epithelial cells and into organ systems.

Assessing the potential adverse effects of the nanomaterials inside cell tissue is the target of the next phase of the ASU research, Westerhoff said.