Biomedical Engineering Reference
In-Depth Information
methylphosphonate), with rapid response and recovery times on the
scale of seconds. The sensor surface is self-regenerating; samples
maintain a constant response with no need for sensor refreshing
through at least 50 gas exposure cycles. The authors claimed that
this remarkable set of attributes makes CNTFET sensors based on
ss-DNA decorated nanotubes very promising for electronic nose and
electronic tongue applications ranging from homeland security to
disease diagnosis.
Forzani
. [281] reported a method to functionalize SWCNTs
in an FET device for the selective detection of heavy metal ions. In
this method, peptide-modified polymers were electrochemically
deposited onto SWCNTs and the selective detection of metal ions
was demonstrated by choosing appropriate peptide sequences. The
signal transduction mechanism of the peptide-modified SWCNT
FETs was studied. It was observed that there was a shift toward the
negative direction of the gate potential upon exposure to Ni
et al
2+
ions.
This negative shift was due to weakening of the interactions of the
oligopeptides with the SWCNTs.
9.5.3
Electrochemical Sensors
CNTs have some important advantages for fabricating carbon
material-based electrochemical sensors including the good electrical
conductivity, the biocompatibility, the large specific area, the well-
defined nanotube structure, the modifiable surface, the functional
groups on the surface with pre-treatment, and the capability of
being solubilized or dispersed in solutions. Based on these unique
properties, a large variety of research works and reviews [15] have
been dealt with CNT-based electrochemical sensors. An extensive
review on the electrochemical CNT-based sensors for applications
has been proposed by Hu and Hu [283].
An electrochemical sensor is mainly composed by a three-
electrode cell with a working electrode (e.g., the new carbon
nanomaterial to be assessed), a reference electrode (e.g., Ag/AgCl for
aqueous media, Ag/Ag
+
for nonaqueous solutions), and an auxiliary
electrode (counter electrode) principally consisting of a material
similar to the working electrode. The electrodes are commonly
immersed in a specific solution of one or more electrolytes for
measuring the characteristic current-potential curves in the cyclic
voltammetry.
