BIOMEDICAL AND BIOMEDICINE APPLICATIONS OF CNTs - Bio-Inspired and Nanoscale Integrated Computing - page 491

CNT-based nanobiosensors may be used to detect DNA sequences in the
body [15, 16]. These instruments detect a very specific piece of DNA that may be
related to a particular disease. Such sensors enable detection of only a few DNA
molecules that contain specific sequences; thus, the patient can be diagnosed as
having specific sequences related to a cancer gene. The use of nanotube-based
sensors will avoid problems associated with the current, much larger implantable
sensors (which can cause inflammation) and can eliminate the need to draw and
test blood samples. The devices can be administered transdermally (through the
skin) avoiding the need for injections during space missions. Biosensors can also
be used for glucose sensing. CNT chemical sensors for liquids can be used for
blood analysis (for example, detecting sodium or finding pH value). CNTs can
also be used as flow sensors.
Ghosh et al. [17] found that the flow of a liquid on bundles of SWNTs induces
a voltage in the direction of flow. This finding can be used in the future in
micromachines that work in a fluid environment, such as heart pacemakers that
need neither heavy battery packs nor recharging. Flow sensors can also be used for
precise measurements of gases utilized by respiratory apparatuses during surgery
and for automatic calculation of medical treatment fees based on output data
leading to reduced hospital costs and more accurate calculation. In summary, the
advantages of CNT-based sensors are that they are less sensitive to variations in
temperature (compared to silicon piezoresistors), which enables them perform
better in many of the biomedical sensing applications mentioned above. Also,
their unique flow sensing properties can be exploited in making heart pacemakers.
As CNT-based sensors are smaller in size, they consume less power, avoid chances
of inflammation, and eliminate the need to draw and test blood samples. They can
be used in detecting very specific pieces of DNA by utilizing their electron transfer
characteristics and functionalization properties. This can help in detecting
important cancerous genes and biomolecules such as antibodies associated with
human autoimmune diseases.
18.3.1.3. Probes. Probes are devices that are designed to investigate
and obtain information on a remote or unknown region or cavity. There are
many studies that have reported the use of CNTs for making probes [18-24].
CNTs are highly suitable materials for AFM probes, as the AFM-generated
image is dependent upon the shape of the tip and surface structure of the sample
of interest. An optimal probe should have vertical sides and a tip radius of
atomic proportions. AFM tips made of silicon or silicon nitride are pyramidial in
shape and have a radius of curvature around 5 nm. In comparison, nanoprobes
made of CNTs have high resolution, as their cylindrical shape and small tube
diameter enable imaging in narrow and deep cavities. In addition, probe tips made
of CNTs have mechanical robustness and low buckling force. Low buckling force
lessens the imaging force exerted on the sample and therefore can be applied for
imaging soft materials such as biological samples. Besides, these factors enhance
the life of probes and minimize sample damage during repeated hard crashes into
substrates [25].