Posted: September 18, 2006

Detecting cancer with silica nanoparticles

(Nanowerk News) Tumor necrosis factor-alpha (TNF-α) is a widely accepted biomarker for cancer, but the minute amounts of this protein circulating in blood makes detecting the molecule and measuring its concentration accurately a technological challenge. Using silica nanoparticles labeled wiTNF-αth the molecule guanine, researchers at the Pacific Northwest National Laboratory have now created a simple and inexpensive electrochemical method that TNF-α at clinically useful levels. Moreover, this assay is amenable to miniaturization, suggesting that it could be easily incorporated into a microfluidics-based assay system.
Reporting its work in the journal Analytical Chemistry ("Sensitive Immunoassay of a Biomarker Tumor Necrosis Factor-α Based on Poly(guanine)-Functionalized Silica Nanoparticle Label"), a research team headed by Yuehe Lin, Ph.D., TNF-α loaded guanine molecules onto the surface of silica nanobeads that also contained a chemical anchor known as avidin. They also attached biotin, which binds with extraordinary strength to avidin, to an antibody that binds to TNF-α protein. The researchers attached a second antibody, one that binds to a different part of TNF-α protein, to a carbon electrode, which functions as the electrochemical sensor.
When TNF-α is present in a solution added to the antibody-labeled electrode, it binds to the antibody. Adding the second antibody produces a sandwich around the TNF-α molecule. At this point, the researchers then added their labeled silica nanoparticle, which binds to the antibody-TNF-α sandwich. In a final step, the investigators added a molecule that reacts with the guanines on the nanoparticle, creating an electrical current that the electrode senses. The current flowing into the electrode is proportional to the amount of TNF-α bound to the first antibody. Experiments with this system showed that the limit of detection for the device is approximately 2 picomolar, well within the range needed to detect physiological levels of TNF-α.
Source: National Cancer Institute
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