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October 13, 2005

Nanoparticle enhanced protein detection for medical diagnosis

This is not molecular manufacturing related but improved ability to detect proteins is part of enhanced protein handling that can be part of a protein based assembler.

Northbrook, Illinois-based Nanosphere is preparing to launch a diagnostic system that uses nanoparticles to detect various proteins at a level of sensitivity never before seen. Scientists know that a protein called prostate-specific antigen, or PSA, is linked with some forms of breast and ovarian cancer. But levels of PSA are so low in women that they're impossible to detect with existing technology. Nanosphere researchers say their technology can do the trick.

"In the end, molecular biology is about amplification," said Northwestern University nanotechnologist Chad Mirkin, who is a co-founder of the company and sits on its board of directors. "If you can amplify a signal that's happening on the cellular level to the point where you can detect it at the human level, you can do great science." The Nanosphere system increases the sensitivity for detecting recognized proteins by six orders of magnitude. "Nobody else can get close to that," Mirkin said.

Nanosphere hopes to have a PSA screen ready by next year for breast and ovarian cancer as well as prostate cancer. Doctors now test for PSA in men using the ELISA protein assay, which costs hundreds of dollars per test and requires high concentrations of the protein to be successful.

At the heart of Nanosphere's unique system are silver-coated nanoballs. Each ball is attached to a synthetic probe designed to bind with a specific protein. If a patient sample contains the protein of interest (for example, a protein linked to a particular type of cancer), it will be sandwiched by the silver nanoparticle and a larger, magnetized metal ball.

A magnet then removes the metal balls, carrying the target proteins and the highly reflective silver spheres along with it. Light reflected from the sample reveals the concentration of the target protein in the patient, even if only a few molecules are present in the sample.

Several emerging companies are trying to create amplification technologies based on quantum dots, another nanotechnology that causes fluorescence in the presence of specific proteins. But those companies aren't yet at the point of considering a mass-market product. Another startup, called Nanoplex Technologies, is also developing a system using metallic nanospheres for protein and nucleic-acid detection, but it is concentrating on the scientific research market, not clinical diagnostics.

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