Biomedical Engineering Reference
In-Depth Information
They reported the fabrication and testing of near-infrared sensors to
detect glucose in the blood using the SWCNTs that modulated their
emission in response to the adsorption of specific biomolecules. A
range of concentration for glucose from 1 to 10 mM was successfully
investigated. Two distinct mechanisms of signal transduction based
on fluorescence quenching and charge transfer were considered
for sensing devices. The results demonstrated new opportunities
for optical sensors based on CNTs operating in strongly absorbing
media of relevance to medicine and biology.
CNTs have been integrated into the MEMS and NEMS [308] for
detection of the physical (force, pressure, strain, temperature) and
chemical quantities (gas concentration). Hierold [308] reported on
two different geometries of MEMS devices based on suspended CNTs
structures integrated in silicon and membrane CNTs transducers
fabricated onto SiO
/Si or Al
O
/Si substrates with an electrodes gap
2
2
3
of 1.5
[309], in collaboration
with Siemens AG, developed a MEMS gas sensor based on individual
suspended SWCNTs for NO
ยต
m. The same group of Hierold
et al.
gas detection. Detection of 180 ppm NO
2
2
was preliminarily reported with a long response time and recovery
time of the device. Sensing mechanisms based on physisorption and
Schottky barrier effects were introduced to explain the gas response.
Zribi
suspended CNT-based resonant
MEMS sensor with a range of detection (0-15 vol.%), linearity in the
response at room temperature, and a detection limit of 0.2 vol.%.
Teh
et al
. [310] reported a CO
2
. [311] reported an MEMS sensor coated by polypyrrole/
carbon nanotube composite for glucose detection in the range up to
20 mM, that is of interest for biological applications.
A nonexhaustive summary of the other principal transducers
used in the CNT-based gas sensors is reported in the Table 9.8.
et al
Table 9.8
Summary of the other principal transducers employed in the
gas sensors using CNTs active layer to detect targeted gases/
analytes or volatile compounds
Materials/
methods
Transducer
Target analyte
Main performance
Ref.
Chemicapacitor
SWCNTs
Chemical vapors,
DMMP
CR: 10-3000 ppm Vapors
CR: 300 ppb-3 ppm
DMMP
DL: <1 ppm Vapors;
DL: ~0.5 ppb DMMP;
OT: RT
Rst: <5 s; Rct: <4 s
[299]
(
Continued
)
