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DNA-wrapped carbon nanotubes
serve as sensors in living cells
Kloeppel, Physical Sciences Editor
photo to enlarge
Strano, a professor of chemical and biomolecular engineering,
and his research team's discovery opens the door to
new types of optical sensors and biomarkers that exploit
the unique properties of nanoparticles in living systems.
— Single walled carbon nanotubes wrapped with DNA can be placed
inside living cells and detect trace amounts of harmful contaminants
using near infrared light, report researchers at the University of Illinois
at Urbana-Champaign. Their discovery opens the door to new types of
optical sensors and biomarkers that exploit the unique properties of
nanoparticles in living systems.
“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 structure and shifting the nanotube’s
natural, near infrared fluorescence to a lower energy.
“The change in emission energy indicates how many ions bind to
the DNA,” said graduate student Daniel Heller, lead author of
the Science paper. “Removing the ions will return the emission
energy to its initial value and flip the DNA back to the starting form,
making the process reversible and reusable.”
The researchers demonstrated the viability of their measurement technique
by detecting low concentrations of mercury ions in whole blood, opaque
solutions, and living mammalian cells and tissues – examples where
optical sensing is usually poor or ineffective. Because the signal is
in the near infrared, a property unique to only a handful of materials,
it is not obscured by the natural fluorescence of polymers and living
“The nanotube surface acts as the sensor by detecting the shape
change of the DNA as it responds to the presence of target ions,”
Co-authors of the paper with Strano and Heller are graduate student
Esther Jeng and undergraduate students Tsun-Kwan Yeung, Brittany Martinez,
Anthonie Moll and Joseph Gastala. The work was funded by the National
To reach Michael Strano, call 217-333-3634; e-mail: email@example.com.