February 2005

Dr. Nanotech vs. Cancer

James Heath has a better way to fight cancer: tiny silicon wires that could sniff out early signs of the disease.

By Philip Ball

If you are among the third of the population who will someday develop cancer, your body will contain warning signs well before your doctor is able to diagnose the disease. If these subtle signals in your cells and your bloodstream could only be detected sooner, you'd have a far greater chance of surviving. The problem is that the changes that mark the early stages of cancer are remarkably complex -- and often slight, even on a molecular level.

But James Heath, a physical chemist at the California Institute of Technology, believes that nanotechnology could finally provide the solution to this molecu­lar riddle. Heath is betting that banks of ultrasmall silicon wires, each made to detect a specific cancer-related protein, could pick up even the most subtle changes in our body chemistry. The nanosensors that Heath and his Caltech coworkers are developing will simultaneously look for hundreds or even thousands of different biomolecules in, say, a drop of blood. If they work, these nanosensors could be the basis for cancer tests that are not only more accurate but, because they don't involve tissue sampling and lab analysis, cheaper and more convenient than those now available.

That's not saying much, of course. Screening for most cancers remains primi­tive, often involving simple physical exams to find evidence of tumor growth, or crude imaging methods such as mammography and x-rays. Blood tests exist for a few cancers, such as prostate and ovarian cancers, but their performance is woeful; not only are they slow and costly, but they're notoriously unreliable. To diagnose prostate cancer, for ex­ample, doctors look for a protein called PSA (prostate-specific antigen) in the blood. But only 25 to 30 percent of men who go through the immensely stressful process of having tissue biopsies because of high PSA levels in their blood actually have prostate cancer. "PSA is always in the prostate," points out Heath, "and is leaked out into the blood in small quantities all the time. When there is some sort of trauma to the prostate -- which could be cancer or something else -- it leaks out in greater quantities. But it is a very poor marker for early-stage prostate cancer, since there really isn't too much trauma to the prostate at that stage."

A more accurate cancer test would better reflect the complexity of biomolecular events. Heath's ambition is to construct devices that can not only make multiple measurements at once, from a drop of blood or a few cells taken from a particular tissue, but also detect extremely small quantities of biomolecules. "We are trying to develop a finger prick–based test," he explains. "We would like this test to eventually be something analogous to what is used for diabetics. Diabetics can now monitor their glucose levels, and because they can do that on a regular basis, they take control of the disease. We would like to develop a similarly enabling platform for cancer."