"This is the first nanotube-based sensor that can detect analytes at the subcellular level," said Michael Strano, a professor of chemical and biomolecular engineering at Illinois and corresponding author of a paper to appear in the Jan. 27 issue of the journal Science. "We also show for the first time that a subtle rearrangement of an adsorbed biomolecule can be directly detected by a carbon nanotube."
At the heart of the new detection system is the transition of DNA secondary structure from the native, right-handed "B" form to the alternate, left-handed "Z" form.
"We found that the thermodynamics that drive the switching back and forth between these two forms of DNA structure would modulate the electronic structure and optical emission of the carbon nanotube," said Strano, who is also a researcher at the Beckman Institute for Advanced Science and Technology and at the university's Micro and Nanotechnology Laboratory.
To make their sensors, the researchers begin by wrapping a piece of double-stranded DNA around the surface of a single-walled carbon nanotube, in much the same fashion as a telephone cord wraps around a pencil. The DNA starts out wrapping around the nanotube with a certain shape that is defined by the negative charges along its backbone.
When the DNA is exposed to ions of certain atoms -- such as calcium, mercury and sodium -- the negative charges become neutralized and the DNA changes shape in a similar manner to its natural shape-shift from the B form to Z form. This reduces the surface area covered by the DNA, perturbing the electronic s
Contact: James E. Kloeppel, Physical Sciences Editor
University of Illinois at Urbana-Champaign