"Smart Dust" Could Aid Drug Research

Originally Published MDDI October 2002

R&D DIGEST

Dust-size chips of silicon created by researchers at the University of California, San Diego, show promise for a range of commercial uses in research and medical laboratories, including the development of rapid biochemical assays and the screening of new drugs. What makes the particles "smart dust" is the way a specific wavelength of light, or color, reflects from them when thin layers of surface films react chemically to a specific chemical or biological agent.

The dust is created by starting with silicon wafers similar to those used in making computer chips. The chips are encoded by generating nanometer-thick layers of porous films on the wafers using a special electrochemical etch. This layered structure on the dust-sized particles, which are produced by using ultrasound to break apart the wafer, gives them their unusual optical properties. The resulting micro-size photonic crystals can reflect light of very precise colors. Each one functions in a manner similar to a single bar of a bar code.

The colors produced by the particles in response to exposure to separate chemicals range from visible to infrared. They are so sharp that a laser can read thousands of distinct colors. The researchers say that this enables the coded particles to perform thousands of biochemical assays in a small beaker or a Petri dish. They speculate that this would be useful in a number of applications, including drug discovery, disease diagnosis, and the controlled release of therapeutic drugs.

Fabricated from silicon, which has good biocompatibility, the particles can be made using existing computer chip technology. And the compatibility of porous silicon with living cells and the long-term stability and nontoxicity of this material could make the chips especially useful in biomedical applications.

According to Frédérique Cunin, a postdoctoral fellow at UCSD, "The use of these encoded silicon nanostructures in medical diagnosis may be significantly better than other methods that involve the use of potentially toxic materials, such as heavy metals." Sangeeta N. Bhatia, MD, associate professor of bioengineering at UCSD, adds that, "This is an example of marrying microtechnology, which is used to make microelectronic chips, with silicon chemistry and molecular and cell biology to create hybrid integrated chip platforms for medical applications."

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