"We have a chip that has many different spots of DNA on it that are designed to recognize all of the possible barcodes that are in the mixture," Mirkin says. "It binds the right spot and provides a signal that can be easily read with a screener."
Instead of a price popping up, a color signal appears, showing the presence of a specific disease.
Although not publicly available yet, Mirkin's test has been very successful in spotting the target proteins, often referred to as biomarkers, for a variety of diseases, in lab experiments. He says, "Biomarkers for lots of different diseases, including prostate cancer, come in the form of proteins."
Prostate cancer was, in fact, the first disease they pitted their nano-particles against. The second leading cause of cancer deaths for American men, prostate cancer is one of several serious illnesses that can be detected early if doctors see higher levels of certain proteins in the blood. For prostate cancer, levels of the protein prostate-specific antigen, or PSA can signal the disease. But, "after treatment for prostate cancer, normally PSA cannot be detected again until it reaches a fairly high threshold. So with this test, PSA can be accessed at much lower levels to say the cancer is coming back and treat it," Mirkin says.
A similar biomarker in the blood has now been identified for ovarian cancer.
More recently Mirkin's test has picked up extremely low concentrations of a protein related to Alzheimer's disease. "The marker is found in the brain, but it's not much use when you can only test for it with a brain biopsy," he explains. "We now know it is also present in spinal fluid."
With many other disease biomarkers that could be detected, Mirkin hopes his test will one day allow doctors to test for dozens of diseases at the same time, and give patients results in a matter of minutes.
This research has been published in Talanta, 15 September, 2005, and the 15 February, 2005, issue of Proceedings of the National Academy of Sciences. It was funded by the National Science Foundation, the National Institutes of Health, and the U.S. Department of Defense.