September 18, 2006
Detecting Cancer with Silica Nanoparticles
Tumor necrosis factor-alpha (TNF-æ) 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 with the molecule guanine, researchers at the Pacific Northwest National Laboratory have now created a simple and inexpensive electrochemical method that detects TNF-æ 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 researchers 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-æ 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-æ molecule. At this point, the researchers then added their labeled silica nanoparticle, which binds to the antibody-TNF-æ 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-æ 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-æ.
This work is detailed in a paper titled, “Sensitive immunoassay of a biomarker tumor necrosis factor-æ based on poly(guanine)-functionalized silica nanoparticle label.” This paper was published online in advance of print publication. An abstract of this paper is available at the journal’s website.