Nanoparticles multitask

2:53pm, September 11, 2007
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Nanoparticles can play many roles, but they're more often used for tagging and sorting molecules rather than for participating in chemical reactions. Nanoscale bits with magnetic properties, for instance, can enhance magnetic resonance images and can tag other molecules in chemical assays. But researchers have now shown that nanoparticles of magnetite (Fe3O4) can play an active chemical role with catalytic muscle applicable to wastewater treatment and biomedical assays.

The nanoparticles can catalyze the same reactions prompted by peroxidases, enzymes that can clean up wastewater and also help researchers detect small amounts of molecules in diagnostic medical assays. Though previously unknown, the chemistry of the magnetite nanoparticles makes sense, report Sarah Perrett and her colleagues at the Chinese Academy of Sciences in Beijing. The nanoparticles are comparable to a mixture of iron ions and hydrogen peroxide—known as Fenton's reagent—that oxidizes organic pollutants so that they can be removed from wastewater.

Assuming that the nanoparticles were chemically inert magnets, researchers working on biomedical assays have previously coated them with a variety of catalysts. Such catalysts produce a color change or other detectable effect by reacting with another molecule in the assay.

Perrett's team has now found, however, that magnetite nanoparticles are 40 times as effective as a commonly used peroxidase in catalyzing a reaction that turns the chemical 3,3,5,5-tetramethylbenzylidine blue. The team reports the finding in the September Nature Nanotechnology.

Because the nanoparticles are less fragile than peroxidases, they could be used under pH and temperature conditions that would destroy the enzymes. Utilizing both the magnetic and catalytic properties of the nanoparticles could streamline biomedical assays, Perrett says.

She and her colleagues have already designed such an immunoassay. "The assay would be worth developing commercially, because it is cheaper, faster, more direct, and potentially more sensitive," Perrett says.

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