Jan 27, 2009
Tunnel current signals read base composition of DNA
DNA sequencing relies on chemical labels to signal the presence of particular bases. Our paper "A hydrogen-bonded electron-tunneling circuit reads base composition of unmodified DNA" describes how the base composition of DNA oligomers can be read by tunneling via a probe functionalized with a complementary base.
How it works
The DNA is trapped onto the surface of a first electrode, modified with chemically-tethered guanidinium ions. These form hydrogen bonded attachments to the phosphate backbone of the DNA. A second probe, functionalized with a DNA base, is approached to the trapped molecule, and then withdrawn as the electron tunneling signal is read.
The characteristic shape of the current versus distance signal identifies the type of base-pairing between the probe and the DNA on the surface. This demonstrates that the base composition of DNA can be read electronically, without the need for chemical labels.
New approach to chemical detection
The present, STM-based arrangement is not suitable for sequencing and does not resolve single bases, but it points the way to a new scheme for electronic sequencing. More generally, it lays out an entirely new approach to chemical detection of one, or a few molecules. That is the trapping of the target molecule in a tunnel gap where one electrode is functionalized with a first recognition reagent, and the second electrode is functionalized with a second reagent. If the two recognized sites are close together, the molecules bonded into the gap will form a tunneling circuit, signaling the very specific detection of the target molecule.
About the author
Stuart Lindsay is Director of the Center for Single Molecule Biophysics at Arizona State University, and Edward and Nadine Carson Professor of Physics and Chemistry.