Nanotechnology. Written in Nano.

Chad Mirkin, director of the International Institute of Nanotechnology at Northwestern University, and his colleagues are changing the future of diagnostic medicine with two nanoscale technologies. The first, called bio-bar-code assays, relies on nanoparticles designed to attach themselves to specific disease-causing proteins; these will vastly improve a doctor’s ability to detect diseases like cancer and Alzheimer’s in their early stages and to identify pathogens like anthrax. The second technology, called dip-pen nanolithography, works like an array of minuscule fountain pens that lay down lines 15 nanometers wide of practically any soluble material on a surface. The idea is to lay down a tiny strip of genetic material on a chip, to which only specific pieces of DNA can bind, and then stick a sensor on each side of it. If the target germ is present, its DNA will adhere to the strand on the chip and change its chemical properties, thereby triggering a warning signal.

Dip-pen nanolithography will allow researchers to prepare the highest-density gene chips the world has ever seen. A Holy Grail in this area is to create one chip capable of detecting any DNA sequence. To do this, one needs a spot of DNA for every possible combination of a 17-base-long sequence [enough to identify key elements of a germ genome]. That’s 417, or nearly 20 billion spots. With current microscale technology, this chip would be the size of a tennis court or at the very best a large-car parking space—too big to ever be practical. But with the resolution afforded by dip-pen nanolithography, one can prepare that kind of sensor chip in an area about the size of a penny.

Bio-bar-code assays have been used to detect biological markers for HIV, Alzheimer’s disease, mad cow disease, prostate cancer, and ovarian cancer. They will have major applications in blood screening, bioterrorism defense, infectious-disease screening, and cancer research. Conventional technology does not have the sensitivity to identify such markers in the blood, let alone to quantify their amounts. Once it is completely developed, such sensor technology should make it possible for a doctor or other individual to screen a patient for many infectious and genetic diseases in the course of an ordinary office visit.