A cluster of carbon nanotubes coated with a thin layer of
protein-recognizing polymer form a biosensor capable of using
electrochemical signals to detect minute amounts of proteins, which
could provide a crucial new diagnostic tool for the detection of a
range of illnesses, a team of Boston College researchers report in
the journal Nature Nanotechnology.
The nanotube biosensor proved capable of detecting human
ferritin, the primary iron-storing protein of cells, and E7
oncoprotein derived from human papillomavirus. Further tests using
calmodulin showed the sensor could discriminate between varieties
of the protein that take different shapes, according to the
multi-disciplinary team of biologists, chemists and physicists.
Molecular imprinting techniques have shown that polymer
structures can be used in the development of sensors capable of
recognizing certain organic compounds, but recognizing proteins has
presented a difficult set of challenges. The BC team used arrays of
wire-like nanotubes approximately one 300th the size of a human
hair coated with a non-conducting polymer coating capable of
recognizing proteins with subpicogram per liter sensitivity.
Central to the function of the sensor are imprints of the
protein molecules within the non-conducting polymer coating.
Because the imprints reduce the thickness of the coating, these
regions of the polymer register a lower level of impedance than the
rest of the polymer insulator when contacted by the charges
inherent to the proteins and an ionized saline solution. When a
protein molecule drops into its mirror image, it fills the void in
the insulator, allowing the nanotubes to register a corresponding
change in impedance, signaling the presence of the protein,
according to co-author Dong Cai, an associate research professor of
Biology at BC.
The detection can be read in real time, instead of after days or
weeks of laboratory analysis, meaning the nanotube molecular
imprinting technique could pave the way for biosensors capable of
detecting human papillomavirus or other viruses weeks sooner than
available diagnostic techniques currently allow. As opposed to
searching for the HPV antibody or cell-mediated immine responses
after initial infection, the nanotube sensor can track the HPV
protein directly. In addition, no chemical marker is required by
the lebel-free electrochemical detection methods.
“In the case of some diseases, no one can be sure why someone is
ill,” said Cai. “All that may be known is that it might be a virus.
At that time, the patient may not have detectable serum antibodies.
So at a time when it is critical to obtain a diagnosis, there may
not be any traces of the virus. You’ve basically lost your chance.
Now we can detect surface proteins of the virus itself through
molecular imprinting and do the analysis.”
