Nano Chemical and Biosensors

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					                           Nano Chemical and Biosensors

                             M. Meyyappan
                           NASA Ames Research Center
                          Moffett Field, CA 94035 USA

Carbon nanotubes (CNTs) have shown interesting electronic, mechanical, optical, thermal, and other
properties and therefore have been pursued for a variety of applications by the nanotechnology
community ranging from electronics to nanocomposites. We have been pursuing development of
chemical and biosensors using carbon nanotubes for the last several years and this talk will present
our progress to date.

In the case of chemical sensors, we use an interdigitated electrode as a chemiresistor, where purified
single-walled carbon nanotubes (SWCNTs) serve as the conducting medium. When the
chemiresistor is exposed to a gas or vapor, the change in resistance is recorded; if SWCNTs do not
respond to a particular gas or vapor, then doping or functionalization strategies are used. A sensor
array is constructed with 32-96 sensor elements with chemical variations across the sensor array. In
the sensor training mode, a pattern of resistance changes is generated from the sensor array for a
particular analyte at a given concentration and humidity level; this needs to be repeated for various
concentrations and humidities and the generated information is stored for later use. In the
identification mode, a pattern recognition algorithm is used to identify that analyte from the
background using the information stored during training. This talk will present examples from our
work to demonstrate the functioning of the sensor. This sensor has also been miniaturized and
integrated in an iPhone which will be described.

In the case of the biosensor, a " lock and key " approach is used wherein a preselected probe for a
given target is attached to the tip of a carbon nanofiber (CNF). CNFs in a patterned array are grown
using plasma chemical vapor deposition on a silicon wafer which serve as individual, freestanding,
vertical electrodes. This nanoelectrode array (NEA) can use DNA, aptamer and antibody probes, and
electrochemical impedance spectroscopy is used upon probe-target binding for signal analysis.
Results will be presented for identification of e-coli and ricin using this NEA. In collaboration with
our Korean colleagues, we have also developed a silicon nanowire based bioFET on 200 mm wafers
and biosensing results from this platform for future lab-on-a-chip needs will be described. The
focus of this effort is to develop nano sensors for “ smart home “ for the elderly and disabled as a
part of the U-Health initiative at POSTECH with key attributes of personalized, predictive and
preventive care.

The author thanks all past and present NASA Ames colleagues for their contributions to the
application development efforts, especially Jing Li, Yijiang Lu, and Jessica Koehne; Prof. Jeong-Soo
Lee and Nano group students at POSTECH, S. Korea.

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