2. In this presentation you will go through the introduction to nanotechnology, some basic
concepts about the nanofabrication approaches and techniques, virus display for
nanowire formation, TMV as template for nanowire scaffold and a little bit about the
self assembly , the advantages and disadvantages of biotemplating and future aspects.
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3. As we all know what is nanotechnology â the study of the controlling matter on the
atomic and molecular scaleâ. Nanotechnology is very diverse ranging from the extensions
of conventional device physics to completely new approach of self assembling. On the
similar basis we can define nano biotechnology ânano bio technology is the engineering
of biological scaffolds at molecular levelâ. Most of the processes of nanotechnology are
integrated with biology or with the use of biological materials. We will see in the further
slides how we can use biological materials to manufacture some regular geometries and
commercial materials.
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4. But we need to distinguish slightly between the nanotechnology and molecular
manufacturing (mostly miss used) nanoscale technology is the use of big
machines to make smaller products while the molecular manufacturing is an
anticipated future technology based on Feynmanâs vision of factories using
nanomachinaries to build complex products. It promises to bring great
improvements in the cost and performance of manufactured goods, while
making possible a range of products impossible today. Every manufacturing
method is a method for arranging atoms. Most methods arrange atoms crudely;
even the finest commercial microchips are grossly irregular at the atomic scale.
Many of todayâs nanotechnologies face the same limit. Chemistry and biology,
however, make molecules defined by particular arrangements of atoms â
always the same numbers, kinds, and bonds. Chemists do this using clever tricks
that donât scale up well to building large, complex structures. Biology, however,
uses a more powerful method: cells contain molecular machines that read digital
genetic data to guide the assembly of large molecules (proteins) that serve as
parts of molecular machines
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5. Top-down and bottom-up are two approaches for the manufacture of products. These
terms were first applied to the field of nanotechnology by the Foresight Institute in 1989
in order to distinguish between molecular manufacturing (to mass-produce large
atomically precise objects) and conventional manufacturing (which can mass-produce
large objects that are not atomically precise). Bottom-up approaches seek to have
smaller (usually molecular) components built up into more complex assemblies, while
top-down approaches seek to create nanoscale devices by using larger, externally-
controlled ones to direct their assembly. The top-down approach often uses the
traditional workshop or microfabrication methods where externally-controlled tools are
used to cut, mill, and shape materials into the desired shape and order. Micropatterning
techniques, such as photolithography and inkjet printing belong to this category.
Bottom-up approaches, in contrast, use the chemical properties of single molecules to
cause single-molecule components to (a) self-organize or self-assemble into some useful
conformation, or (b) rely on positional assembly. These approaches utilize the concepts
of molecular self-assembly and/or molecular recognition. Such bottom-up approaches
should, broadly speaking, be able to produce devices in parallel and much cheaper than
top-down methods, but could potentially be overwhelmed as the size and complexity of
the desired assembly increases
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6. This slide just compares the scale of things made by nature or made by man. Man took
many centuries to learn the ways of nature making the nanoscale materials but still
there are many challenges comes across. Broadly speaking we can classify
nanotechnology under three headings âwetâ, âdryâ and computational nanotechnology.
Wet Nanotechnology: which is the study of biological systems that exist primarily in
water environment?
Dry Nanotechnology: which derives from surface science and physical chemistry e.g.
structures of carbon, silicon etc.
Computational Nanotechnology: This permits the modeling and simulation of complex
nanometer scale structures.
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7. The most top down fabrication technique is nano lithography. In this process, required
material is protected by mask and the exposed material is etched away.e.g.
Photolithography, Electron and ion based lithography and scanning probe lithography.
Bottom up approach utilizes the concept of molecular self assembly or molecular
recognition and taking the advantage of physicochemical interactions for the hierarchical
synthesis of orders nanoscale structures.
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8. There are two basic ways for nanosynthesis and these are physical and chemical
methods.
In chemical methods we have :
Sonochemistry
Microwave synthesis
Hydrothermal methods
Solgel methods
Wet chemical coprecipitation etc
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9. At about 550 million years ago, organisms began to have their simple organic molecules
in order to grow more complex organic matrices which precisely fit form to function.
One of the first âbioinspiredâ archtectural projects was the contruction of the crystal
palace (1851).In 20th century , scientist began to take a more active interest in nano-
biological world. The father of this approach was R.J.P williams (oxford University), who
instigated a study of the detailed functional use of inorganic elements in biological
systems.
Mann (oxford university) gave the understanding of bio mineralization in terms of
movement and precipitation of inorganic elements within a âbiologicalâ system.
The complexity of biological structures and complex systems which give rise to them are
not easily replicated that convinced scientists to directly utilize the natural occurring
materials.
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10. Biotemplating is the study of biological scaffolds at the nanoscale the important example
are DNA, Viruses and bacteria.
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11. Bio systems have inherently developed very specific molecular recognition patterns that
can be manipulated through genetic control. It also can be used to exert molecular scale
control over nucleation, growth, and stabilization of inorganic materials, analogous to
the process of biomineralization. Furthermore, due to the remarkable capability of
biological molecules to self-assemble at multiple length scales, the opportunity exists for
designing novel nanomaterials via genetic modification and then constructing
hierarchically assembled structures. The combination of biological self-assembly and
biosynthesis of nanomaterials can enable us to create entirely new concepts
applications and devices.
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12. Biotemplating seeks to either replicate the morphological characteristics and the
functionality of a biological species or use a biological structure to guide the assembly of
inorganic materials. In the first case, the biological substrate has interesting
morphological characteristics (e.g., diatoms, butterfly wing scales, viruses) and metal
replication is used to provide a more stable and more controllable synthetic substrate.
The replication process typically leads to the
generation of either a negative, positive (or hollow), or exact copy of the template.
Indeed, a large variety of biological species have been used as templates: bacteria,
textiles/paper, hair, cells, insect wings, spider silk, wool, and wood. The majority of the
biological structures that have been used for replication show nanoporous features (e.g.,
diatoms), channels (viruses), and other complex hierarchical architectures (butterfly
wings). The level of precision in replicating nanoscale topographies and features is the
major challenge. In the second case concerning the biologically guided assembly of
nanomaterials, a natural biological system is used to nucleate inorganic structures and
promote pattern formation. This is ubiquitously directed by
covalent/noncovalent interactions and molecular recognition processes. For such
interactions to take place, the biological structures must present specific
physicochemical and/or morphological attributes to direct the assembly of inorganic
structures into technologically useful platforms. Such attributes can include a secluded
inner channel or inner cavity that is accessible only by molecules of specific size/charge,
or the presence of a unique functional group at specific locations.
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13. There is already quite a long list of biological materials that have been successfully
replicated for the formation of artificial structures, and these include cotton/cloth, pine
wood, human and animal hair, silk, and wool, viruses, bacteria, DNA and proteins.
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14. The video is taken from :www.youtube.com (with the title virus)
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16. Virus Display with Inorganic Materials:
(a) A combinatorialvirus library is obtained or synthesized that expresses random
peptide fusions (color shaded areas).
(a) The virus library is exposed to a substrate (typically an inorganic single crystal) and
positive binding interaction of
the peptide fusion is allowed to occur with the substrate.
(c) After washing the virus interactions with detergents to ensure specific binding to the
substrate, the successful binding viruses are isolated via a disruption in binding
conditions, typically using a change in pH. The isolated viruses are amplified in their
bacterial host and reintroduced to a fresh substrate surface. The process between (b)
and (c) is repeated several times with the isolated and amplified viruses, mimicking an
evolutionary cycle.
(d) Once the (b) to (c) cycle is complete (typically 3 rounds), the DNA from the virus is
isolated and sequenced to determine the identity of the peptide responsible for binding
to the substrate.
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17. The M13 phage pIII constructs used in the selection experiments, with the peptide
displayed only on one end of the filamentous phage, were used in the first M13-based
nanocrystal growth studies. In particular, two phage-bound peptide sequences that were
selected for ZnS, named Z8 and A7, were shown to control ZnS particle size and shape at
room temperature, under aqueous conditions.
Wild-type clones (no peptide insert) were used as a control. Transmission electron
microscopy (TEM), high resolution TEM (HRTEM), scanning TEM (STEM) and electron
diffraction (ED) data revealed that the addition of a ZnS-specific phage clone affected
particle size and formed discrete ZnS crystals. Crystals grown in the presence of the Z8
clone were observed to be approximately 4 nm in size of the zinc blende phase. For the
A7 virus, nanocrystals grown were 4 nm by 2 nm in size of the wurtzite crystal phase.
Particles grown without the ZnS-specific phage clones or with wild type clones were
non-crystalline and were much larger (100â500 nm) in size distribution.
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18. Schematic diagram depicting an engineered M13 virus displaying peptides to direct
nucleation of inorganic materials and/or further assemble viruses into complex
heterofunctional arrays.
(a) M13 virus, with peptides fused to pIX shown ingreen, to pVIII shown in orange, and
to pIII shown in blue.
(b) Nanoparticles represented as spheres localized on the viruses illustrate the potential
of multiple materials engineering into one viral structure, whose length and shape can
be custom-tailored depending on the genome size engineered.
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19. An overall advantage to this genetic programming approach to materials engineering, in
addition to materials-specific addressability, is the potential to specify viral length and
geometry. The length of a filamentous virus is related to the size of its packaged genetic
information and the electrostatic balance between the pVIII-derived core of the virion
and the single-stranded DNA.
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20. Additionally, viruses can be conjugated with one-dimensional nanowires/nanotubes,
two dimensional nano electrodes, and microscale bulk devices. One-dimensional
materials, such as nanotubes or nanowires, when conjugated with the pIII end of M13
viruses, may form phase separated lamellar structures that have inorganic nanotube or
nanowire layers and phage building block layers.
Two-dimensional nano-thick plate shaped electrodes can be organized. Alternative
cathode and anode structures might be useful for future nanosize biofuel cells. When
the specific binding M13 virus is combined with micro-size objects, periodic organization
of these micro-dimensional objects is also possible
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31. Self-assembly is a term used to describe processes in which a disordered system of pre-
existing components forms an organized structure or pattern as a consequence of
specific, local interactions among the components themselves, without external
direction
Distinctive features: At this point, one may argue that any chemical reaction driving
atoms and molecules to assemble into larger structures, such as precipitation, could fall
into the category of SA. However, there are at least three distinctive features that make
SA a distinct concept.
Order:First, the self-assembled structure must have a higher than the isolated
components, be it a shape or a particular task that the self-assembled entity may
perform. This is generally not true in chemical reactions, where an ordered state may
proceed towards a disordered state depending on thermodynamic parameters.
Interactions:The second important aspect of SA is the key role of weak interactions (e.g.
Van der waals, pi-pi attractions, hydrogen bonds) with respect to more "traditional"
covalent, ionic or metallic bonds. Although typically less energetic of a factor 10, these
weak interactions play an important role in materials synthesis. It can be instructive to
note how weak interactions hold a prominent place in materials, but especially in
biological systems, although they are often considered marginally with respect to
"strong" (i.e. covalent, etc.) interactions. For instance, they determine the physical
properties of liquids, the solubility of solids, the organization of molecules in biological
membranes.
Building blocks: The third distinctive feature of SA is that the building blocks are not
only atoms and molecules, but span a wide range of nano- and mesoscopic structures,
with different chemical compositions, shapes and functionalities. These nanoscale
building blocks (NBBs) can in turn be synthesised through conventional chemical routes
or by other SA strategies.
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32. Self-assembly has a fundamental advantage over mechanically directed assembly: It
requires no machinery to move and orient components, letting random, Brownian
motion do the job instead. Selective binding between uniquely matching surfaces
compensates for the randomness of the motions that bring components together.
Molecular synthesis methods and self-assembly can be used to produce atomically
precise nanosystems by the billions, and even by the ton, thereby establishing a
technology base with wide-ranging applications that can drive development forward.
The architecture of biomolecular fabrication is based on the use of programmable
machines to produce the complex parts necessary for self-assembly of complex systems.
The same fundamental architecture can be extended to use artificial biomolecular
machines (and then non-biomolecular machines), resulting in products made of better
and more diverse engineering materials.
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33. The most fundamental disadvantage of pure self-assembly is that for every product, the
structure of the parts must encode the structure of the whole. This requires that
components be more complex, which tends to make design and fabrication more
difficult. Another consequence is that a self-assembled product will be partitioned by
complex internal interfaces that have no operational function. Unless they are
strengthened after assembly, these interfaces will weak. These are major constraints.
Mechanically directed assembly avoids these constraints. Because components need not
encode the structure of a product, they can be simple and standardized, and they can be
chosen for their functional properties with less concern for how they are put together.
This will enable more straightforward design and fabrication, but one must make the
necessary machinery â and I expect that this will be accomplished by means of self-
assembly.
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34. Linear single-stranded DNA templates have been used to direct the ordered assembly of
Au nanoparticles tagged with Complementary oligonucleotides. But it canât be used to
make more complex structures. Hence, synthetic DNA molecules featuring branched
junction motifs have been designed. âSticky endsâ flanking the junctions enable the self-
assembly of these novel DNA sequences into 2D and 3D architectures, such as lattices
and grid. DNA nanotechnology is an area of current research that uses the bottom-up,
self-assembly approach for nanotechnological goals. DNA nanotechnology uses the
unique molecular recognition properties of DNA and other nucleic acids to create self-
assembling branched DNA complexes with useful properties.
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35. There are two types of self-assembly, intramolecular self-assembly and intermolecular
self-assembly. Most often the term molecular self-assembly refers to intermolecular
self-assembly, while the intramolecular analog is more commonly called folding. (folding
is the process by which a molecule assumes its shape or conformation. The process can
also be described as intramolecular self-assembly where the molecule is directed to
form a specific shape through noncovalent interactions, such as hydrogen bonding,
metal coordination, hydrophobic forces, van der Waals forces, pi-pi interactions, and/or
electrostatic effects.)
The fig at the bottom shows the micelle formation by self assembly of detergent
molecules and protein molecules. The hydrophobic tails are arranged in such a way to
form a micelle with protein core.
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36. Notable advantages of biotemplating in nanostructure fabrication include the sheer
structural diversity of available biological species and materials, as well as the
sophisticated architectures (1D, 2D, and 3D) and degree of complexity achievable.
Together, these elements provide for the creation of a diverse range of novel materials
with an unprecedented repertoire of dimensions (resolution <100 nm) and
morphologies that extend beyond what is currently possible with conventional
lithography/ etching techniques. The biotemplating approach is also potentially more
cost- and time-effective (parallel fabrication
approach) when compared with current serial techniques (e.g., electron beam
lithography, X-ray lithography) for nanostructure fabrication. In addition, the repetitive
topochemical features and variety of functional groups found in many biological
materials, can be exploited for the in situ synthesis and directed self-assembly of both
organic and inorganic nanostructures under mild conditions without the use of harsh
chemical treatments. And finally, biotemplates
are also highly amenable to very (spatially) precise modifications at the molecular level
through rational genetic engineering and/or targeted chemical modifications. Taken
together, these attributes lead to a âbiomolecular tool-kitâ that offers great diversity and
a facile approach for the fabrication of a variety of structures and devices. The full range
of possibilities that biological templates have to offer has only just started to be
explored. Indeed, researchers are just beginning to grasp an understanding of the effects
of nanoscale topographies on the optical, chemical, and electrical properties of
materials. On the basis of these initial reports, there is clearly great potential for using
biological materials to develop entirely new types of sensing systems
that display superior selectivity and sensitivity over existing conventional designs.
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37. However, for biotemplating to become more established as a reliable
nanofabrication approach, several limitations that currently exist will need to be
overcome. Most notably, as the biotemplating technique is a relatively new
approach, it still lacks the high yield levels and precise uniformity provided by
other synthetic fabrication methods. In particular, large-scale fabrication may be
an issue in some cases because of a lack of sufficient quantities of purified
biological material, or because of a lack of long-range order in the final product
due to intrinsic lattice/morphological defects in the biotemplate itself. Moreover,
because the exact mechanisms by which biological entities form defined patterns
and direct the growth of crystalline materials are not yet fully understood,
biotemplating studies are often conducted in a highly empirical manner. This
often requires a significant amount of effort to be spent in trial and error
experiments, with results that are in some cases neither predictable nor always
repeatable. Finally, there remains a great need for scientists to develop a better
understanding of the biological-materials interface in general. Current surface
functionalization methods for the creation of engineered substrates for the
deterministic, oriented attachment of biological molecules still lack the degree of
control necessary to be useable on a large scale, such that high quality and high
uniformity can be reproducibly achieved.
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38. Biotemplating also poses a number of substantial intellectual challenges. The brief
summary of these challenges is that we do not yet know how to do it, and cannot even
mimic those processes known to occur in biological systems at other than quite
elementary levels. Although there are countless examples of Biotemplating materials all
around us--from molecular crystals to mammals--the basic rules that govern these
assemblies are not understood in useful detail, and processes cannot, in general, be
designed and carried out "to order" and to solve these issues we need a
multidisciplinary approach.
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