Using silica nanoparticles labeled with the molecule guanine, scientists at the Pacific Northwest National Laboratory have now created a simple and inexpensive electrochemical method that detects tumor necrosis factor-alpha (TNF-alpha) 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, a research team headed by Yuehe Lin, Ph.D., 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 the TNF-æ protein. The scientists attached a second antibody, one that binds to a different part of the TNF-æ protein, to a carbon electrode, which functions as the electrochemical sensor.

When TNF-alpha 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-alpha molecule. At this point, the scientists then added their labeled silica nanoparticle, which binds to the antibody-TNF-alpha sandwich. In a final step, the researchers 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-alpha 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-alpha.


Posted by: Andria    Source

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