Discovery of a "Nanoparticle Effect"

Professor Leads Research that Uncovers “Nanoparticle Effect”


A paper co-authored by Bren researchers and published in the Feb. 27 issue of the journal Environmental Science & Technology provides answers to a core question for environmental nanotoxicologists: what is “special” about nanoparticles when compared to their component chemicals?

The research was led by Bren professor of environmental microbiology Patricia Holden, with the majority laboratory research performed by Holden Lab postgraduate researcher John Priester. Funding was provided by the U.S. Environmental Protection Agency as well as the NSF- and EPA-funded UC Center for the Environmental Implications of Nanotechnology (UC CEIN).

The project was aimed at defining the effects of cadmium ions versus cadmium selenide (CdSe) quantum dots (QDs)—engineered nanoparticulate semiconductors with applications ranging from medical diagnostics to photovoltaics—on environmental bacteria, and how bacteria change the QDs.

“With their increased use, engineered nanomaterials (ENMs) will enter the environment, where they may be altered by bacteria and affect bacterial processes,” say the authors. “Metallic ENMs, such as cadmium selenide (CdSe) quantum dots(QDs), are toxic due to the release of dissolved heavy metals, but the effects of cadmium ions versus intact quantum dots are mostly unknown.”

A key finding was that low concentrations of cadmium ions and QDs similarly inhibited bacterial growth, but QDs were more toxic than cadmium ions when higher concentrations were studied, even in the presence of cadmium ions. QDs, which were highly reactive outside the cells, became more reactive, and destructive, when associated with cells. QDs entered the cells and accumulated, reaching concentrations far in excess of those outside cells.

“We don’t expect bacteria to readily take up ENMs, as they are too large to pass through the membrane”, says Holden, “but QDs damaged the membranes, enabling QDs to pass into cells, where they were potent toxicants.”

The research was accomplished through a collaboration involving colleagues from UCSB’s Department of Chemistry and Biochemistry (Professor Galen Stucky and postdoctoral researcher Peter Stoimenov), the Materials Research Laboratory (Jin Ping Zhang), the Department of Earth Science (doctoral student Chris Ehrhardt), the Jet Propulsion Laboratory, and the Stanford Synchrotron Radiation Laboratory.

Says Holden: “Research into the biological fates and effects of engineered nanomaterials requires the strengths of a variety of disciplines, and we organized our effort to use the best available technologies and experts to get the answers. Now that we know that these nanoparticles have a specific and profound effect—a ‘nanoparticle effect’—on bacteria, our next goal is to determine why. Understanding ‘why’ can make it possible to ‘design out’ negative effects, which is key to environmentally safe use of nanomaterials.”