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1. Carbon Nanotubes (CNTs)Carbon Nanotubes (CNTs)
By: Naghmeh Poorinmohammad

2. OUTLINE
• Introduction
• Properties
• Synthesis Methods
• Applications (general and biotechnology-related)
• Challenges
• Summary
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3. INTRODUCTION
• Carbon nanotubes (CNTs) are hexagonally shaped arrangements of
carbon atoms that have been rolled into tubes.
• Diameter: less than 1 nm.
• Length: from a few nanometers up to a millimeter.
• Rolling up a graphene sheet may lead to a CNT (For imagination only!).
Adopted from “http://www.physik.uni-regensburg.de”
what are they?
INTRODUCTION: HistoryINTRODUCTION
What are they?
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4. INTRODUCTION: History
• 1952:
Radushkevich and Lukyanovich showed hollow graphitic carbon fibers
with 50nm diameter.
• 1979
Abrahamson presented evidence of carbon nanotubes at the 14th Biennial
Conference of Carbon at Pennsylvania State University.
• 1981
A group of Soviet scientists published the results of chemical and structural
characterization of carbon nanoparticles produced by a thermocatalytical
disproportionation of carbon monoxide.
• 1991
Nanotubes discovered in the soot of arc discharge at NEC, by Japanese
researcher Sumio Iijima.
INTRODUCTION
History
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5. INTRODUCTION: CNT types
(n,m)
n= column
m= row
If:
n=m  Armchair
n≠m  Chiral
(n,0)  Zig-Zag
INTRODUCTION: HistoryCNT types
Based on symmetry
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6. INTRODUCTION: CNT types
Multiple Wall CNT
or
Single Wall CNT
or
Parchment model Russian doll model
INTRODUCTION: HistoryCNT types
Based on walls
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7. PROPERTIES: Mechanical
• Carbon nanotubes are the strongest, flexible and stiffest materials yet
discovered in terms of tensile strength and elastic modulus respectively.
• The hardness (152 Gpa) and bulk modulus (462–546 Gpa) of carbon
nanotubes are greater than diamond, which is considered the hardest material.
• The current Young’s modulus value of SWCNs is about 1 terapascal.
• The modulus of the multi walled carbon nanotubes correlates to the amount
of disorder in the carbon nanotube walls.
• when multi walled carbon nanotubes break, the outermost layers break first
Materials Young’modulus(Tpa) Tensile strength(Gpa) Elongation at
break(%)
SWNTE ~1 (from 1 to 5) 13-53 16
Armchair
SWNTT
0.94 126.2 23.1
Zigzag SWNTT 0.94 94.5 15.6-17.5
Chiral SWNT 0.92
MWNTE 0.2-0.8-0.95 11-63-150
Stainless steelE 0.186-0.214 0.38-1.55 15-50
KevlarE 0.06-0.18 3.6-3.8 ~2
EExperimental observation; TTheoretical prediction
INTRODUCTION: HistoryPROPERTIES
Mechanical
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8. PROPERTIES: Electrical conductivity
• CNTs can be metallic or semi-conductors due to their geometry.
• For a given (m,n) nanotube:
- If n=m (armchair)  the CNTS is metallic
- If n-m is multiple of 3  the CNTs is semiconducting with a
small band gap.
- Otherwise ,the CNTs is moderate semiconductor.
• In theory, metallic nanotubes can carry an electric current density of
4 × 109 A/cm2, which is more than 1,000 times greater than those of
metals such as copper.
• They are one dimensional conductors only along the axis
INTRODUCTION: HistoryPROPERTIES
Electrical conductivity
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9. PROPERTIES: Thermal conductivity
• SWNTs room-temperature thermal conductivity is about 3500 W/(m·K) and
over 3000 W/(m·K) for individual MWNT.
• Addition of nanotubes to epoxy resin can double the thermal conductivity for a
loading of only 1%, showing that nanotube composite materials may be useful
for thermal management applications.
• All nanotubes are expected to be very good thermal conductors along the tube,
but good insulators laterally to the tube axis.
INTRODUCTION: HistoryPROPERTIES
Thermal Conductivity
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10. PROPERTIES: Thermal conductivity
• Flourescence:
 Semiconducting SWCNTs emit and absorb NIR.
 No excitonic luminescence in metallic tubes.
 Photoluminescence is used for measuring the quantities of semiconducting
nanotube species in a sample.
 Also to identify the symmetry and (n,m) properties.
• Raman spectroscopy:
 Raman spectroscopy has provided an exceedingly powerful tool for
characterization of CNT’s with respect to their diameters, and quality of the
samples properties.
 SWCNT and MWCNT can be discriminated via this method.
INTRODUCTION: HistoryPROPERTIES
Optical
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11. SYNTHESIS
• The most common and perhaps easiest way to produce CNTs.
• Carbon contained in the negative electrode sublimates because of the
high-discharge temperatures.
• The yield for this method is up to 30% by weight and it produces both
single- and multi-walled nanotubes with lengths of up to 50 micrometers
with few structural defects.
• Produces a complex mixture of components, and requires further
purification - to separate the CNTs from the soot and the residual catalytic
metals present in the crude product.
INTRODUCTION: HistorySYNTHESIS
I. Arc discharge method
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12. SYNTHESIS
• A substrate is prepared with a layer of metal catalyst particles, most commonly
nickel, cobalt, iron , or a combination.
• The substrate is heated to approximately 700°C.
• two gases are bled into the reactor: a process gas (such as ammonia , nitrogen or
hydrogen ) and a carbon-containing gas (such as acetylene , ethylene , ethanol or
methane ).
• Nanotubes grow at the sites of the metal catalyst; the carbon-containing gas is broken
apart at the surface of the catalyst particle, and the carbon is transported to the edges
of the particle, where it forms the nanotubes.
• Attracted attentions for its feasibility and potential for large-area production with
reasonable growth rates at relatively low temperatures.
INTRODUCTION: HistorySYTHESIS
II. Chemical vapor deposition (CVD)
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13. SYNTHESIS
• A pulsed laser vaporizes a graphite target in a high-temperature reactor while an
inert gas is bled into the chamber.
• Nanotubes develop on the cooler surfaces of the reactor as the vaporized carbon
condenses.
• A water-cooled surface may be included in the system to collect the nanotubes.
• The laser ablation method yields around 70% and produces primarily single-
walled carbon nanotubes with a controllable diameter determined by the reaction
temperature .
• However, it is more expensive than either arc discharge or chemical vapor
deposition.
INTRODUCTION: HistorySYNTHESIS
III. Laser ablation
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14. APPLICATIONS
• More slender tips  higher resolution will gain in microcopy.
• In addition, due to the high elasticity of the nanotubes, the tips do not suffer from
crashes on contact with the substrates.
• Biological molecules, such as DNA can also be imaged with higher resolution using
nanotube tips, compared to conventional STM tips.
INTRODUCTION: HistoryAPPLICATION
I. AFM/STM Tips
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Tang et al., Nano Lett. 5(1), 11-14 (2005).
Si Tip
CNT Probe
Chang et al., Jpn. J. Appl. Sci. 43(7B), 4517-4520 (2004).
Chang et al., Jpn. J. Appl. Phys. 43(7B), 4517-4520 (2004).

15. APPLICATIONSINTRODUCTION: HistoryAPPLICATION
II. Filters/membranes
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16. APPLICATIONS
• An important issue in intracellular drug delivery is the poor permeability of
the plasma membrane to many drugs.
• Thus, various carriers, including polyethylene glycol, peptides and lipids,
have been developed to facilitate the cellular entry of drugs.
• Recently, the feasibility of using SWNTs for intracellular drug delivery has
been demonstrated.
• They have high drug loading capacities and good cell penetration
qualities.
• Problems: lack of solubility, clumping occurrences, and half-life
INTRODUCTION: HistoryAPPLICATION
III. Molecular carriers
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17. APPLICATIONS
• Semi-conductive SWNTs with appropriate chirality can generate a small
band gap fluorescence of 1 eV, which corresponds to NIR range (900-1600
nm).
• Biological tissues have very low absorption, scattering, and
autofluorescence in this range and therefore, are very useful for biological
imaging.
• CNTs show great promise in NIR photoluminescence imaging , Raman
imaging and optical absorption agent for photoacoustic imaging.
INTRODUCTION: HistoryAPPLICATION
IV. Biomedical imaging
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18. APPLICATIONS
• A biosensor is a bioanalytical
device consisting of 2
components:
a bioreceptor and a transducer.
• The bioreceptor is a
biomolecule that recognizes the
target analyte whereas the
transducer converts the
recognition event into a
measurable signal.
INTRODUCTION: HistoryAPPLICATION
V. Bio-sensing
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19. • SWNT biosensors can exhibit large changes in electrical impedance and
optical properties in response to the surrounding environment which is
typically modulated by adsorption of a target on the CNT surface.
• Low detection limits and high selectivity require engineering the CNT surface
(e.g., functional groups and coatings).
• CNT plays dual role in a biosensor both as immobilization matrices and as
electron mediator.
V. Bio-sensing
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20. CHALLENGES
• Cost: Too expensive (~ $ 200per gram)
• Toxicity: there are some reports showing CNTs can
damage DNA or causing pulmonery toxicity.
• Manipulation: hard to purify and the ability to
manipulate structures at the atomic scale.
• Large-scale production: Large quantity fabrication
process still missing.
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21. SUMMARY
• CNTs have special properties which makes them interesting
in many fields.
• There is still a great need of improving its production and
manipulation.
• In biotechnological applications, we must care especially
when studying them for biomedical applications.
• Using CNTs for us biotechnologists needs a team work
since a deep knowledge will be gained when working in
interdisciplinary discipline!
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22. • Shao, Wei, et al. "Carbon Nanotubes for Use in Medicine: Potentials and
Limitations." (2013).
• Ajayan, Pulickel M., and Otto Z. Zhou. "Applications of carbon
nanotubes."Carbon nanotubes. Springer Berlin Heidelberg, 2001. 391-425.
• Balasubramanian, Kannan, and Marko Burghard. "Biosensors based on
carbon nanotubes." Analytical and bioanalytical chemistry 385.3 (2006):
452-468.
• Popov, Valentin N. "Carbon nanotubes: properties and
application." Materials Science and Engineering: R: Reports 43.3 (2004):
61-102.
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KEY REFERENCES

23. Thank You
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