M.D. on a Chip  ScienCentral News, 2/6/03, by Ann Marie Cunningham Next time you feel sick, your doctor might use your blood sample, plus one tiny computer chip, to rule out up to 10,000 diseases—all while you're still there in the office.As this ScienCentral News video reports, scientists have designed a new chip that could help you and your doctor find out what's wrong much sooner. Medical handwriting that's easy to read Chad Mirkin, a chemist at Northwestern University, says a major problem with today’s medical care is “we don’t have technology that’s powerful enough or simple enough” to allow your doctor to diagnose an illness during your office visit. Mirkin set out to change diagnostics with a new, inexpensive gene chip. This chip carries the DNA, or the genetic material, of specific disease agents. Once exposed to a blood, urine, or saliva specimen from a patient, the genetic material recognizes any infection, and signals a diagnosis through the chip to a computer monitor in a doctor’s office. Mirkin is a nanotechnologist, which means he seeks scientific solutions at the scale of just a few atoms. So he turned first to a technique developed by the computer industry to make tiny silicon chips. Computer chip manufacturers call this technique photolithography. The process involves making a photographic mask of the pattern of circuits you want to put on a wafer-sized chip, and then using light to trigger a chemical reaction that will trace your pattern on the chip. But photolithography cannot work very well at the incredibly small nanoscale that Mirkin wanted. He needed to write directly on a chip. Mirkin developed his own writing technique, using the atomic force microscope, an instrument that has made possible many key advances in nanotechnology. An atomic force microscope has a sharp tip made of silicon or ceramic and is only a few atoms wide. The tip can bounce over the surface of atoms, the way a steel phonograph needle bounces over a vinyl record, providing scientists with three-dimensional photographs on the atomic scale. The tip also can move atoms around. Working from a computer, a scientist types in directions on the keyboard, and watches the tip’s movements on the monitor. Mirkin uses the tip like a calligraphy pen, dipping it first in an “ink” made up of water and DNA strands of disease agents. Then he “writes” with the ink-coated tip on a chip, transporting DNA molecules onto the surface. The result is a gene chip that he foresees will be useful to genetics laboratories, as well as in medical diagnosis. In fact, he says it will be possible to put an entire genome on one chip. Mirkin’s goal is to write on a chip with as many “pens” as possible, in order to make chips that could recognize the DNA of any possible disease. By collaborating with Chang Liu, an electrical and computer engineer at the University of Illinois at Urbana-Champaign, his team has developed a pen writing systems that allows one to make chips that, in a matter of minutes, could recognize as many as 10,000 diseases – while you sit in your doctor’s waiting room. Dr. Mirkin’s work is funded by the National Science Foundation, the Defense Advanced Research Projects Agency (DARPA), and the U.S. Air Force Office of Scientific Research.