Researchers develop tool to analyze 'Nature's Carriers'

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LOS ALAMOS, N.M., July 17, 2000 - Researchers at the Department of Energy's Los Alamos National Laboratory and the University of New Mexico have developed an inexpensive, versatile system that characterizes the properties and behavior of colloids, tiny particles that play crucial roles in everything from drug delivery to mineral separation to transport of contaminants.

The information gained from the Automated Video Microscopic Imaging and Data Acquisition System (AVMIDAS) may have wide-ranging applications in the pharmaceutical/medical, mineral separation, materials science, environmental remediation and other industries.

"AVMIDAS can help researchers better understand colloidal characteristics as they interact with each other and attach themselves onto, and detach from, solid-liquid and gas-liquid interfaces," said lead developer Amr Abdel-Fattah of Los Alamos' Environmental Technology Group. "AVMIDAS also can precisely characterize colloids in terms of their bulk concentrations and electric potential at their surfaces," added Abdel-Fattah. Paul Reimus, also of the Environmental Technology Group, and Mohamed El-Genk of the University of New Mexico helped develop the automated system.

"Understanding the dynamics behind colloidal attachment and detachment to surfaces is critical," said Abdel-Fattah. "For example, colloidal attachment determines how effectively medical drugs carry corrective proteins to human tissue and how efficiently precious metals are separated from the rest of the rocks."

Colloids range in size from one billionth to one millionth of a meter and are inside all living things and in the air, water and soil in such forms as smoke and dust particles, mineral fragments, bacteria, proteins and biological cells. In some cases, actinides and other chemical species form colloidal particles or attach themselves to colloids, which behave differently from larger particles and smaller species in that they sometimes can move larger distances in shorter periods of time.

AVMIDAS combines video techniques, a modified version of dark-field microscopy and specially designed image processing and data extraction software in one interactive tool. First, a suspension of colloids is placed in a test cell and illuminated from below by a 300-watt halogen bulb. Between the test cell and the bulb are a dark-field condenser and iris diaphragm, which lets through only the minimum amount of light needed to illuminate the colloids against a dark background for easy visualization under the microscope.

A charge-coupled device camera situated on top of the microscope takes pictures of the colloids' movements at about 30 frames a second, about the same speed as a typical video camcorder. The images are transferred to a computer and digitized, where software designed by Abdel-Fattah processes the images and performs multi-parameter analyses simultaneously.

Almost instantaneously, the concentrations of colloids, rates of attachment and detachment on particular surfaces, and even duration of attachment of individual colloids are displayed on the computer screen in real time.

"There is no other system available today that can do the full range of colloidal analyses that AVMIDAS is capable of," said Abdel-Fattah. "Some systems can perform single-parameter analysis, but they cost $50,000 or more. AVMIDAS could be marketed for approximately $16,000."

He added, "The system is fully automated, so human errors in data collection and analysis are greatly reduced. In fact, even those without extensive knowledge of particle physics can operate AVMIDAS."

Abdel-Fattah and his colleagues developed AVMIDAS over a two-year period as part of the Nevada Test Site's Underground Test Area Program to study colloidal transport of actinides in subsurface fractures at NTS. A patent is pending.

More news releases from the Environmental Science and Waste Technology (E) Division