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Contents:
• Design of Medical Nanodevices
• Methods of Nanomaterials Fabrication
 Top-Down Approach
 Bottom-Up Approach
• Synthesis of Metallic Nanoparticles and
Applications
• Synthesis of Semiconductor
Nanoparticles and Applications
• Synthesis of Oxide Nanoparticles and
Applications
•
•
•
•
•
Vapor Phase Reactions
Solid-State Phase Segregation
Heterogeneous Nucleation
Kinetically Confined Synthesis
Synthesis of Carbon Nanotubes and
Applications
• Conclusions
Design of Medical Nanodevices
• The design of nanorobots requires the culmination of
various scientific fields ranging from quantum mechanics
to kinematics analysis.
• Materials used for the construction could be carbon,
hydrogen, silicon, fluorine, sulfur, polimer, lipids, etc.
depending on the interaction with the environment.
• Nanorobots must be able to perform their task or job
without being too much influenced by their surroundings,
i.e. pH.
• At the same time, when used in medicine, these
nanorobots must be undetected by the immune system
and operate like any other normal structures composing
the human body.
Roadmap in Developing
Nanomachines
• Step 1. Developing the nanocomponents which include
power supplies, fuel buffer tanks, sensors, motors,
manipulators, on-board computers, pumps, pressure tanks
and structural support.
• Step 2. Assembling of nanorobots which includes
making complex assemblies from the nanocomponents
with nanoscale precision. Ideally the assembling would
be performed by bionanorobots which have ability to
build the nanomachines from available reserves or
supplies, to repair damaged parts, to sense environment
and respond appropriately, and so forth.
Roadmap in Developing
Nanomachines (continued)
• Step 3. Artificial intelligence, This would require development in
basic computational capabilities, and rules would have to be
established so that bionanomachines can make quick and sharp
decisions at the nanoscale level. Nanocomputers, communicational
and navigational equipment will have to be developed in order to
establish communication between the nanorobots and outside
world. This will allow us to program swarm behavior. All these
capabilities will form the basic principle of a nanorobot with
artificial intelligence.
• Step 4. Self-assembling and self-evolution. Bioswarms will have
ability to self-assemble and self-evolve, and would manage energy
efficiently.
Examples of Design at Nanoscale
• The vast numbers of natural molecular machines are proteinbased.
• Naturally, proteins are used to perform various cellular tasks.
• Biocomponents are a rational choice for designing nanorobots.
• Molecular manufacturing is the process of building machines
at the atomic or molecular level.
• One example of a realistic approach in manufacturing to
nanorobots for medical purposes is biochips, which are a
collection of nanoarrays arranged on a solid substrate.
• The advantage of using biochip is that they allow numerous
tests at the same time. Biochips are able to identify biological
components and perform thousands of biological reactions in
only several seconds.
Methods of Nanomaterials Fabrication
• Two techniques are used for the synthesis of nanomaterials.
• The first is the top down approach which uses nanoscale imprinting
and milling techniques to create nanostructures out of bulk materials.
• The second is the bottom-up approach which uses basic chemistry
techniques to build atom-by-atom and assemble nanostructures.
• For synthesizing nanoparticles in particular, the top-down approach
employs milling and repeated thermal cycling as primary techniques.
• Bottom-up techniques allow a variety of different approaches to be
used, making this for nanoparticle synthesis far more common. These
techniques include heterogeneous nucleation on substrates, phase
segregation through annealing solids at high temperatures, confining
particles in a small space using chemical reactions, and other
thermodynamic and kinetic approaches.
Top-Down Approach and Applications
• Milling produces nanoparticles from bulk materials at sizes larger than 20 nm.
Limitations include that the particles have a broad size distribution and varied
shape, may contain impurities from the milling medium, and may have defects
resulting from milling.
• Applications of nanoparticles produced from this process are the fabrication of
nanocomposites and nanograined bulk materials. One example uses a highenergy ball milling process for synthesis of nanocrystalline hydroxyapatite
particles that can be used as bone filler for coating metallic prosthesis, in dental
implants, and for making matrices for controlled drug release applications.
• Repeated thermal cycling produces very fine particles by repeated quenching of
the bulk material. As a result of heating, the material with low thermal
conductivity can be broken into small pieces. This process has limitations:It can
be difficult to design and control, and it is not applicable to all materials.
• Applications. Metal nanopowders, consisting of 25 nm nanosilver or 80 nm
nanoaluminum particles, are produced by heating the metals of interest using
repetitive pulsed electrical arc discharge and plasma in a reactor. Nanosilver
powders can be used in inkjet applications and for their antimicrobial properties
as well. Nanoaluminum powders can be used in making primers, advanced
propellants and explosives.
Bottom-Up Approach
• Homogeneous nucleation is a one method of the bottomup approach.
• It can be used to synthesize nanoparticles in all the three
states: liquid, solid and gaseous.
• Homogeneous nucleation is initiated in a saturated
medium by disturbing the equilibrium of saturation
throught decreasing the temperature of the
solution/medium.
• This will lead to supersaturation, nucleation and growth
of the centers of nucleation in the medium. For example,
when the temperature of a glass matrix is slowly reduced,
quantum dots will be formed due to supersaturation in the
matrix.
Bottom-Up Approach (continued)
• The process of supersaturation of the growth species is governed by two
processes.
• First, the growth species have been generated, diffused in the mixture and
adsorbed on the surface of the growth surface.
• Secondly, there will be surface growth due to irreversible incorporation of
growth species onto the solid surface.
• There are several ways of controlling the nanoparticle growth process, which
can help control the size distribution. The growth control can be achieved by
surface processes such as mononuclear growth, polynuclear growth or by
diffusion-limited growth.
• Mononuclear growth is layer-by-layer growth where one layer of growth is
completed before the formation of another layer starts on the surface.
• In polynuclear growth, the surface process is very fast because of high surface
concentration, which causes the growth of the second layer to start before the
layer is completed. Polynuclear growth is favored over mononuclear growth for
formation of the same-sized nanoparticles, because as particles grow bigger, the
radius difference gets smaller.
• Diffusion-limited growth is the most preferable process for formation of
monosized nanoparticle (i.e., particles of the same size); it can be simply
controlled through “drop-by-drop” addition of the reactant or a variation of the
technique.
Synthesis of Metallic Nanoparticles and
Application
• For synthesis of metallic nanoparticles using homogeneous nucleation
methods, metal complexes are reduced using reducing agents in dilute solutions.
Precursors may include metals, inorganic salts and complexes.
• Some of the common reducing agents used are NaOH, H2O2, CO, P and H2.
And polymer stabilizers like PVA (polyvinyl alcohol) and sodium polyacrylate
are used as well.
• A combination of a diluted low concentration of the reactants in the solution
and polymer stabilizers forming a layer around the nanoparticles results in
diffusion-limited growth and steric stabilization to produce monosized
nanoparticles.
• The kind of reducing agent used can be a factor in deciding the size of
nanoparticle produced, as well as the size distribution.
• Application. The electrochemical deposition method is common for
synthesizing metallic nanoparticles and reflects the same process described
above. This process can produce palladium, nickel and cobalt nanoparticles in
the size range of 1.4 to 4.8 nm. Palladium nanoparticles have applications as
quantum dots and catalysts, and in making filters to remove groundwater
contamination, nanofibers and textiles. Nickel nanoparticles have applications
in making alloys, batteries, magnetic materials and solid oxide fuel cells. Cobalt
nanoparticles have applications as sealants, shock absorption materials, in
manufacturing medical equipment, and in manufacturing radioactive shielding.
Synthesis of Semiconductor
Nanoparticles and Applications
• This process uses pyrolysis of organometallic precursors to
synthesize “non-oxide” semiconductor nanoparticles.
• Pyrolysis is a process of overcoming the activation energy by
increasing the energy of the material using heat.
• Organometallic materials are organic compounds that have at
least one metal-to-carbon bond and are used as catalysts in many
applications.
• Application. Cadmium selenide (CdSe) quantum dots are
synthesized using trioctylphosphine selenide as a precursor.
CdSe quantum dots can be used in manufacturing polymer-based
photovoltaic cells, chemical sensors, optical temperature probes
and emitters for color displays.
Synthesis of Oxide Nanoparticles and
Applications
• This process uses sol-gel processing to synthesize metal oxides
and organic-inorganic hybrid materials.
• Sol-gel preparation uses metal salts as precursors. Catalysts are
then used to promote hydrolysis of these salts.
• This results in a rapid reaction leading to supersaturation of the
growth species. It basically uses temporal nucleation followed by
diffusion-controlled growth principles.
• The size of the nanoparticles produced depends on the
concentration of the reactants and the aging time and can range
from 1 to 100 nm.
• Application. IFC-305 (a novel drug for liver diseases) encapsulated
silica oxide nanoparticles are synthesized using sol-gel processing
for controlled drug delivery.
Vapor Phase Reactions
• Synthesis in the vapor phase usually happens in vacuum conditions
at high temperatures. As a result, low concentrations of growth
species are available as reactants in the diffusion-controlled growth
process.
• The nanoparticles generated are then collected on a lowtemperature non-stick substrate.
• The challenge with this process is that not all nanoparticles will
settle on the substrate. Stabilization to prevent these nanoparticles
from agglomeration is also difficult.
• Application. Gallium arsenide (GaAs) nanoparticles can be
synthesized using this approach. The size range of the particles is
10 to 20 nm. GaAs nanoparticles can be used in quantum dot
applications and a wide variety of electronic and optoelectronic
applications.
Solid-State Phase Segregation
• Metals and semiconductor nanoparticles are synthesized in a
glass matrix using this method.
• Precursors are mixed in a liquid glass melt at high temperatures
during glass making.
• Then the glass is cooled down to the phase transition temperature
for a planned period of time. This causes supersaturated
precursors to form nanoparticles by nucleation and growth
through solid-state diffusion.
• Application. This process is used in formation of nanocrystalline
cobalt aluminate (CoAl2O4) nanoparticles which can be used as an
inorganic ceramic blue pigment for applications in paint, glass,
porcelain enamels and fiber. Its optical properties can also be used
in manufacturing color filters for automotive lamps or luminescent
materials in optical devices.
Heterogeneous Nucleation
• Heterogeneous nucleation reactions take place on a substrate and
for synthesis of quantum dots or nanoparticles. The growth of the
nanoparticles on the substrate can take place in the following
manner:
 If the growth species are more strongly bonded to each other than to the
substrate, they will form ‘islands’ on the substrate, with a group of atoms
sticking together on the substrate. This process is referred to as island
growth.
 If the growth species equally favor strongly binding to the substrate just as
they do to each other, the falling and distribution of the atoms will be layer
by layer, one monosized particle layer at a time before more atoms start to
make another layer above it. This is referred to as the layer growth.
 Island-layer growth is a combination of the above two processes to make a
continuous film. Some atoms will tend stick together and form islands,
whereas others will individually directly stick to the substrate. This will give
a larger size distribution.
Heterogeneous Nucleation
• Homogeneous surface defects that act as nucleation centers need
to be created.
• This can be done using a process like thermal oxidation.
• Oxygen is used in thermal oxidation to form oxide layers on the
surface of the substrate.
• This can be done by heating the substrate such that the oxygen
atoms can diffuse through the substrate surface and form defects.
• Application. Nickel nanoparticles between in the size range 20600 nm with a narrow size distribution can be formed using
homogeneous nucleation process. As mentioned above, nickel
nanoparticles have applications in making alloys, batteries,
magnetic materials and solid oxide fuel cells.
Kinetically Confined Synthesis
• This process deals with stopping the synthesis when we have
achieved our desired products/results.
• This can be accomplished by supplying only a limited amount of
precursor for the reaction, by physically filling up the reaction
space; or by terminating the growth species’ progress by having
organic compounds or alien ions occupy the reaction site.
• One of these techniques is used in growth termination method.
Here, the stop growth method is used for synthesis of monosized
nanoparticles, organic compounds or specific ions.
• Application. This techniques is used to synthesize cadmium sulfide
(CdS) colloidal nanoparticles. The size of the nanoparticles can be
controlled by the concentration of organic ligands introduced to the
system. CdS nanoparticles have applications is optoelectronics.
Synthesis of Carbon Nanotubes and
Applications
• Carbon nanotubes were discovered in the soot of arc discharge in
1991.
• Since then, researchers have successfully developed some
manufacturing techniqures for carbon nanotubes, such as arc
discharge, laser ablation, plasma torch, and chemical vapor
deposition.
• Arc discharge is the most traditional manufacturing method, which
consists of placing acertain amount of inert gas into a vacuum
chamber between the two graphite electrodes. The discharging of
electrodes leads to the formation of soot on the cathode containing
the carbon nanotubes. This method produces both single- and
multiwall nanotubes with lengths of up to 50 micrometers with few
structural defects.
Synthesis of Carbon Nanotubes and
Applications (continued)
• In laser ablation, a graphite target is vaporized by pulsed laser
radiation in a reactor filled by an inert gas. The carbon vapor
condenses on the cooler surfaces of the reactor producing the
nanotubes. This technique provides better control of graphite
ablation and evaporation, and thus is suitable for manufacturing
single-wall carbon nanotubes with a controllable diameter.
• Application. Carbon nanotubes have a wide variety of applications.
In nanomedicine, the single- and multiwall carbon nanotubes
could be used, for example, in cancer diagnostics and treatments.
Nanotubes have a very interesting characteristic that could make
them incredibly useful in dealing with cancer: the nanotubes
naturally penetrate into the cells. This opens up great possibilities
in both drug delivery and diagnosis.
Conclusions
• We have discussed design approaches and methods of fabrication
of medical nanodevices with various types of nanoparticles.
• There are a wide variety of techniques to choose from for
synthesis of nanoparticles.
• We have also discussed different applications that these
nanoparticles are being used in or are being considered for.
• Important points that need to be considered when designing a
synthesis process are:
 Synthesis of nanoparticles is possible in all three phases: liquid, solid and
gaseous.
 Stabilization processes to prevent the nanoparticles from agglomeration are
very important.
 Making a same size distribution of nanoparticles is another important
factor, which can be controlled by diffusion-limited growth processes or by
confining the growth space