The American Cancer Society says that one in six American men will get prostate cancer. But if it recurs after treatment, it can be very difficult to detect. As this ScienCentral News video reports, one nanotechnologist says his new supersensitive test could help spot dangerous cancers much more quickly.
Tiny Trackers for Bio Bar Codes
Prostate cancer is very common: For American men, it is the second leading cause of cancer deaths. Itís 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 or its recurrence. Researchers also are looking into the possibility that in women, elevated levels of PSA might be an early warning of breast cancer.
In men, PSA is produced by the cells of the prostate gland. When it enlarges, PSA levels in the blood can rise. If prostate cancer is diagnosed, it usually can be treated successfully. But current tests for PSA are limited: For example, if prostate cancer recurs after surgery or radiation therapy, PSA can be very difficult to detect.
The prostate-specific antigen protein. image: Protein Data Bank, Rutgers University
At Northwestern University, chemist Chad Mirkin uses nanotechnology to make disease detection faster and more accurate. Director of Northwesternís Institute for Nanotechnology Center, Mirkin already has used miniscule gold particles, each only a few nanometers wide, to develop simple but sensitive new tests for infectious disease and bioterror agents such as anthrax bacteria. [see "Also on ScienCentral News"]
Recently, Mirkin has been focusing on ways to use tiny gold nanoparticles to track down even minute traces of particular protein signals in a patientís blood and monitor their ebb and flow, so that doctors can spot a serious illness like prostate or breast cancer as early as possible. He wanted a test for proteins that worked as well as polymerase chain reaction (PCR), an extremely sensitive tool that molecular biologists use to detect genetic material.
To demonstrate how well such a test could work, Mirkin has come up with a new method for detecting PSA in a patientís blood sample. Mirkin chose to work with PSA because current screening tests are given often, and so researchers know a great deal about how they work. But he emphasizes that his technology is designed to target any protein of interest. The test uses very tiny particles that react with any protein in a patientís blood sample, and release thousands of strands of its DNA. Then this DNA acts as what Mirkin refers to as a ďbio bar code,Ē signaling that a particular protein is present.
This animation shows how Mirkin's PSA detection test works. animation: Donna Vaughan
To find PSA, Mirkin and his research team start by tagging gold nanoparticles with thousands of strands of DNA, along with antibodies that can recognize any PSA in a patientís blood sample. The antibodies on the particles bind to any PSA present. Researchers also tag tiny magnetic particles with antibodies that latch onto PSA. In a patientís specimen, the gold and magnetic particles sandwich any PSA present. Next, the researchers use a magnet to separate all the gold particle/PSA/magnetic particle sandwiches from other molecules in the mix. Then they heat the sandwiches to release the DNA. For every PSA molecule in a patientís blood sample, thousands of DNA strands are released. Researchers can analyze the DNA to determine what type it is, and how much they have found.
Mirkin compares the DNA to ďa bar code for the PSA.Ē As efficiently as a bar code flashes an itemís price through a scanner, the DNA can tell whether there is PSA present, and whether there is enough to signal prostate cancer. Mirkin believes his test also could use ďbio-bar codesĒ to diagnose diseases like Alzheimerís, for which no detection tool exists at present. And his technique could use many bio-bar codes to detect different types of proteins at the same time in one sample, meaning that one simple test could screen for many diseases. Mirkin expects his test to be available to medicine within three years.
Mirkinís work on bio-bar codes has been published in Science (September 26, 2003) and presented at the national meeting of the American Chemical Society (September 11, 2003). His research is funded by the National Science Foundation, the Defense Advanced Research Projects Agency (DARPA), and the Air Force Office of Scientific Research (AFOSR).