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Nanotech News
Three-Layer Magnetic Nanoparticles as DNA Probes Combining the optical and chemical properties of a gold nanoparticle with the magnetic properties of iron oxide nanoparticles, investigators at Northwestern University have created a novel nanocomposite particle that could lead to faster and more sensitive diagnostic assays for cancer biomarkers. These new three-layer nanoparticles, described in a paper published in the Journal of the American Chemical Society, contain a silica core, a layer of iron oxide, and an outer coating of gold. In their efforts to use nanoparticles to create rapid, ultrasensitive diagnostic assays for cancer, researchers have most often relied on gold nanoparticles because of the wealth of chemical methods that are available for attaching a wide variety of detection molecules to the nanoparticle surface. Investigators have also tried using iron oxide nanoparticles because the particles’ magnetic properties would provide opportunities to use a simple magnetic field in some of the purification steps that are part of most every diagnostic assay. However, the chemical methods needed to attach biomarker detection molecules to iron oxide are not simple, and can damage the detection molecules. A team of investigators led by Chad Mirkin, Ph.D., decided to meld the best of both types of nanoparticles, but doing so required a clever chemical approach because iron and gold have proven difficult to combine in a single nanoparticle. The solution was to start with a positively charged silica nanoparticle – silica, or silicon dioxide, is the major component of sand. The positive charge on the silica nanoparticles attracts both negatively charged iron oxide particles and negatively charged gold nanoparticles, holding them in place for a subsequent chemical reaction that converts the gold nanoparticles into a solid coating of gold layered over the iron oxide nanoparticles stuck to the silica core. The resulting composite particles are indeed magnetic and retain the chemical versatility of gold nanoparticles. With little difficulty the investigators were able to attach DNA probe to the surface of the nanocomposite and use it to bind to its complementary DNA sequence. The researchers note that this DNA-composite construct was very stable, an important property that is required for any potential real-world diagnostic reagent. The Northwestern team now plans to evaluate these composite particles in various analytical systems that this group has been developing (see earlier story). This work is detailed in a paper titled, “Three-layer composite magnetic nanoparticle probes for DNA.” This paper was published online in advance of print publication. An abstract is available through the journal’s website. |
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