An
interdisciplinary team from Columbia University that includes
electrical engineers from Columbia’s Engineering School, together with
researchers from the University’s departments of Physics and Chemistry,
has figured out a way to study single-molecule interactions on very
short time scales using nanoscale transistors. In a paper to be
published online January 23 in Nature Nanotechnology, they show how, for
the first time, transistors can be used to detect the binding of the
two halves of the DNA double helix with the DNA tethered to the
transistor sensor. The transistors directly detect and amplify the
charge of these single biomolecules.
Prior
to this work, scientists have largely used fluorescence techniques to
look at interactions at the level of single molecules. These studies
have yielded fundamental understanding of folding, assembly, dynamics,
and function of proteins and other cellular machinery. But these
techniques require that the target molecules being studied be labeled
with fluorescent reporter molecules, and the bandwidths for detection
are limited by the time required to collect the very small number of
photons emitted by these reporters.
The
Columbia researchers, including Professor of Electrical Engineering Ken
Shepard, Professor of Chemistry Colin Nuckolls, and graduate students
Sebastian Sorgenfrei and Chien-Yang Chiu, realized that transistors,
like those used in modern integrated circuits, have reached the same
nanoscale dimensions as single molecules. “So this raised the
interesting question,” said Sorgenfrei, the lead author on the study,
“as to whether these very small transistors could be used to study
individual molecules.”
They
have discovered that the answer is “yes.” The transistors employed in
this study are fashioned from carbon nanotubes, which are cylindrical
tubes made entirely of carbon atoms. While these are still emerging
devices for electronics applications, they are exquisitely sensitive
because the biomolecule can be directly tethered to the carbon nanotube
wall creating enough sensitivity to detect a single DNA molecule.
The
Columbia team expects this new technique to be a powerful tool for
looking at single molecule interactions and is looking at
instrumentation applications that currently rely almost exclusively on
fluorescence such as protein assays and DNA sequencing. They also plan
to study interactions at time scales several orders of magnitude greater
than current techniques based on fluorescence.
“The
area of single molecule research is an important one and pushes the
envelope on our sensing systems,” commented Ken Shepard, Professor of
Electrical Engineering at Columbia Engineering. “There is a huge
potential for modern nanoelectronics to play an important role in this
field. Our work, which has been a terrific collaboration between groups
from Electrical Engineering, Chemistry, and Physics, is a great example
of how nanoelectronics and biotechnology can be combined to produce new,
exciting results.”
Shepard
hopes that this research, which was funded primarily by the National
Science Foundation and the National Institutes of Health, will lead to
exciting new applications for nanoscale electronic circuits.
SOURCE: Columbia University