Doctors cannot detect and diagnose an infectious disease very quickly or easily these days: the necessary means don’t exist.

But as this ScienCentral news video reports, nanotechnology promises to deliver the right tools: minute gold particles that are simple to use, yet powerful enough to detect biological threats anywhere.

Sick Enough to Change Color

Nanotechnologists expect to transform medicine, and along with it, our well-being. At Northwestern University, chemist Chad A. Mirkin noticed that right now, it is often impossible for a doctor to detect, diagnose, and treat a patient with an infectious disease during a single office visit. Currently, both doctor and patient must wait several days before expensive, complicated, slow tests can tell them what’s wrong. In cases of serious illnesses, such as the anthrax attacks of 2001, patients may be dead by the time medicine knows how to treat them.

Mirkin decided to use nanotechnology to develop more powerful technology. By working so small, he could detect many more diseases, much more quickly. His new approach would be inexpensive, yet simple enough for a nurse or physician’s assistant to use, either at a doctor’s office, on a battlefield, at a reservoir, or any other place that may have been contaminated. At the same time, Mirkin’s system is very sensitive - able to detect even very small traces of infection - and very powerful - capable of distinguishing many different kinds of diseases accurately, and diagnosing them simultaneously.

Mirkin starts with gold particles, each only a few nanometers in diameter. To grasp the nanoscale, Mirkin suggests starting with a dime, which is about a millimeter thick. If the dime were sliced into a thousand pieces, each piece would be one micrometer thick, or one thousand nanometers. If that piece were sliced into another thousand pieces, it would then be one nanometer. Each of the gold particles that Mirkin uses is about 13 nanometers wide.

At the nanoscale, all the properties of any material change, including its color. Gold becomes a strong red: “In the Middle Ages,” Mirkin says, “people used gold particles as dyes in stained glass windows.” By varying the size or shape of his particles - for example, using triangles instead of spheres, he can have a vast range of colors available - colors that can translate into codes. If he uses silver, he can create codes in the blue or green range of shades.

Collaborating with experts in materials and genetics, Mirkin’s research group attached miniscule bits of genetic material to the gold particles. “Anything living has a genetic marker,” Mirkin explains, “a fragment of DNA that is unique to it.” The DNA-carrying gold particles recognize the DNA of disease agents. Once the particles are released in a blood, urine, or saliva sample taken from a patient, the genetic material latches on to an infectious agent. After minimal processing, the particles give off color signals that can be read on a monitor. The particles can work like a litmus test for a single agent, giving off a blue signal for positive and red for negative. Or a color code can signal whether many disease agents are present at once.

Mirkin points out that rapid diagnosis is important in any case of infectious illness - and absolutely vital to combat bioterrorism or biowarfare. He is working with Nanosphere, a company that plans to market a toaster-sized version of his new disease detection system that could be part of a mobile defense unit. Eventually, he foresees units the size of today’s Palm Pilots which could remain in doctors’ offices or travel into battle in medics’ backpacks.

His research was supported by the Defense Advanced Research Projects Agency, the Air Force Office of Scientific Research and the National Science Foundation.