BIOMEDICAL AND BIOMEDICINE APPLICATIONS OF CNTs - Bio-Inspired and Nanoscale Integrated Computing - page 490

Silicon piezoresistors have the disadvantage in that their resistance is highly
sensitive to variations in temperature. As CNTs have increased sensitive and a
temperature coefficient almost two orders of magnitude lower than that of
silicon, highly efficient pressure sensors incorporating CNTs can be fabricated.
Fabrication of piezoresistive pressure sensors that incorporate CNTs can bring
dramatic changes in the biomedical industry, as many piezoresistance-based
diagnostic and therapeutic devices are currently in use. Pressure sensors can be
used in eye surgery, hospital beds, respiratory devices, patient monitors, inhalers,
and kidney dialysis machines [11, 12]. During eye surgery, fluid is removed
from the eye and, if required, cleaned and replaced. Pressure sensors measure
and control the vacuum that is used to remove the fluid, and provide input to the
pump's electronics by measuring barometric pressure. Hospital bed mattresses
for burn victims consist of pressure sensors that regulate a series of inflatable
chambers. To reduce pain and promote healing, sections can be deflated under
burn areas. Pressure sensors can also be used for sleep apnea (a cessation of
breathing during sleep) detection. The pressure sensor monitors the changes
in pressure in inflated mattresses. If no movement is found for a certain period,
the sleeper is awakened by an alarm. Pressure sensing technology is used in
both invasive and noninvasive blood pressure monitors. Many patients who use
inhalers activate their inhalers at an inappropriate time, resulting in an insufficient
dose of medication. Pressure sensors in the inhalers identify the breathing cycle
and release the medication accordingly [11, 12]. During kidney dialysis, blood
flows from the artery to the dialysis machine and after cleaning flows back into the
vein. Waste products are removed from the blood through osmosis and move
across a thin membrane into a solution that has the blood's mineral makeup [13].
Using pressure sensors, the operation of the dialysis system can be regulated
by measuring the inlet and outlet pressures of both the blood and the
solution. Intelligent pressure sensing systems play an important role in portable
respiratory devices that consist of both diagnostic (spirometers, ergometers,
and plethysmographs) and therapeutic (ventilators, humidifiers, nebulizers, and
oxygen therapy equipment) equipments. They serve patients with disorders of
asthma, sleep apnea, and chronic obstructive pulmonary disease. They measure
pressure by known fluid dynamic principles.
In [14] CNTs are used as an immobilization matrix for the development of
an amperometric biosensor. The biosensor was developed by growing aligned
MWNTs on platinum (Pt) substrates. The platinum substrate served as the
transduction platform for signal monitoring, whereas opening and functionaliza-
tion of large CNT arrays allowed for the efficient immobilization of the model
enzyme (glucose oxidase in this case). The schematic diagram of the CNT array
biosensor is shown [14]. The arrays were purified by treatments with acid or air.
The acid treatment resulted in the removal of impurities including amorphous
carbon that occurred during the production procedure. The lengths of the
nanotubes were also reduced by approximately 50%. Air oxidation resulted in
the production of thinner nanotubes because of the peeling of the outer graphitic
layers from the nanotubes.