bio-inspired metamaterials - university of new...
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Bio-inspired Metamaterials
Simon ButlerSupervisor: Prof. Rebecca Seviour
2/06/2017
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What is a metamaterial?
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• Defined by the meta atom and its position in the lattice
• Defined by the atom and its position within the lattice
Conventional material Meta material
• It is important to note: Both materials are smaller than the wavelength of interest. This makes them HOMOGENLOUS. The individual units are indistinguishable from the greater structure as a whole.
Convention against Meta: A contrast comparison
• Plane Wave HFSS simulations of infinite sheet.
• Determined S11 S21
• Material Properties determined via a Nicholson-Ross-Weir approach
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EM Simulations
70 nm unit cell
50nm major radius10nm minor radius 25% circumference split
Wave propagation
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Equations
Smith DR, Schultz S, Markos P, Soukoulis CM (2002) Determination of effective permittivityand permeability of metamaterials from reflection and transmission coefficients. Phys Rev B65:195104
Transmission
Reflection
Transmission
Reflection
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Extracted EM parameters
Imaginary
Imaginary
Real
Real
Permittivity
Permeability
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EM Simulations
125 nm unit cell
100nm major radius10nm minor radius 25% circumference split
Wave propagation
Transmission
Reflection
Transmission
Reflection
7
Extracted EM parameters
Imaginary
Imaginary
Real
RealPermittivity
Permeability
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Technique Resolution Cost Limitations Throughput
Optical lithography 15nm $30 million2D,
HighPhotosensitive material
Laser interference lithography 20nm $50,000
2D,
Photosensitive material,
Limits in design
High
Electron beam/Focused Ion Beam lithography 4nm $2000000 2D, Photosensitive material Low
Scanning Tunnelling Microscopy Atomic $30,000 to $50,000
Conductive material, V low
throughput/construction in parallel not possible
due to topological differences on the atomic scale
V. Low
Atomic Force Microscopy Atomic $30,000 to $50,000
V low throughput/construction in parallel not
possible due to topological differences on the
atomic scale
V. Low
Molecular Beam Epitaxy 45nm £150,000Crystalline structures greatly limit design
flexibility, low resolutionHigh
Liquid Phase Epitaxy 50nm £150,000Crystalline structures greatly limit design
flexibility, low resolutionHigh
DNA Origami ~5nm ~£800 Functionalisation. Aggregation. V. High
Conventional fabrication techniques
• Biological has been fabricating EM systems for billions of years.
• DNA has the potential to rapidly produce, in a high throughput manner, nanoscale geometries.
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EM materials in nature
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• Origami refers to folding paper into a fixed final structure.
Brown paper Turns into Science Fox
• DNA origami refers to folding DNA into a fixed final structure.
Scaffold and staples
Turns into
Folded DNA construct
DNA origami - Principals
• Technically in the terms defined earlier this lattice structure as oppose to the functional unit.
• The meta atom will be a single split ring of gold going around the perimeter of the sphere.
• It has a major radius of ~21nm and consists of 7249 base pairs arranged in a 24 layered helices.
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Structure considered
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• Evolution of genetic code requires strict (Or at least very high levels) of conservation during replication.
• The 4 bases will always bind in the predictable A to T C to G.
• Due to the weak hydrogen bonds which stabilise the DNA helix, when heated it will separate, when the temperature is lowered bases in proximity will anneal to their specific Watson Crick partners.
DNA origami - Mechanics
• Individual helices are created and joined by junctions.
• Once complete a sequence is applied to the continuous scaffold.
• Output sequences are then provided for all staples.
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caDNAno - Introduction
100 nanometer line
Castro CE, Kilchherr F, Kim D, Shiao EL, Wauer T, Wortmann P, Bathe M and Dietz H (2011) A primer to scaffolded DNA origami. Nature Methods, 8(3):221-9
• The first design was a single split ring the curvature of the split ring was created by joining 6 separate helices.
• DNA has a helical pitch of 10.5 bases per 360 degree.
• If insertion or deletion events break this rule it will create torsion in the helices. This effect was facilitated to create a C from varying lengths of DNA.
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DNA origami design - caDNAno
• Examples of structures which benefit from simulation include structures which do not rely on general distribution and symmetry in their final design.
• The first design: A single free floating split ring is highlighted above. Further lattice components in this project will always be simulated in this manner pre fabrication.
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Cando
• The second (and current) design is a sphere comprising of 24 helices.
• Unlike the first design there is no, or to be precise very little, tension between helices.
• The curvature is facilitated by a carefully measured ratio of sequence lengths each representing a latitudinal line 1/24th of the way down the sphere.
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DNA origami design - caDNAno
Site specific
• As discussed, technically, the DNA origami units are not the functional units themselves but a lattice which provides structure.
• 2 Strategy types are available for functionalisation – Global and site specific.
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Functionalisation
Site specific strategy Global aggregation strategy
Kuzyk A, Schreiber R, Fan Z, Pardatcher G, Roller E-M, Hogele A, Simmel FC, Govorov AO and Liedl T (2012) Assembly of DNA origami gold nanoparticle helices and principle of circular dichroism. Nature, 483, 311-314
• Fabrication: One pot reaction. Annealing buffer.
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• The Buffer solution encourages base pair annealing and protects DNA during annealing.
• Initial Denaturation occurs at around 90 degrees celsius. This temperature is then gradually lowered as part of a controlled and design specific annealling cycle.
Fabrication Protocols
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Nanolight
• Measuring the diffusion of particles under Brownian motion, with the Stokes-Einstein relationship to determine size distribution of particles
50nm 100nm
Size nm Size nm
Nu
mb
er
Nu
mb
er
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SEM
• Imaging under SEM on silica did not present clear images at this stage.
• Issues are being addressed and the next phase of imaging will begin shortly.
500nm (x100000 maginification)
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AFM
• Imaging under AFM showed high levels of aggregation of SRR structures.
• Silica was shown to be a poor substrate under these conditions and further imaging will be conducted on mica with specific fixing protocols.
• AFM went Bang on last use.
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What next…
• Lattice construction will be attempted by the attachment of complementing sequences.
• Protocols for high yield both in terms of fabrication and functionalisation will be refined.
• Imaging of structures on mica will be pursued.
• Characterisation of material under specific EM frequencies of interest will take place.
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We would like to thank the AFOSR and the EPSRC for there support